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Chapter 1 Force & Pressure
Meaning of force
 Force can be defined as a push or pull on an object. Both non-loving and
living things can exert a force.
 A force can be defined as a push or pull upon an object resulting from the
object interaction with another object.
 For example-Picking, Kicking, Shutting, Squeezing, Pushing, Lifting etc.
 Force can also be defined as an influence that brings about a change in the
speed, direction of motion, or shape of the object.
 In order to move an object from one location to another, there must be a net
force exerted on the object to trigger the object in motion.
 More push is required to move a heavy object in comparison to a lighter
object.

Question Can you lift a bucket of water without holding it?

Answer A pull action is required to lift a bucket. This is provided by the force exerted
by the body holding the bucket. As a result, we need a holding to lift a bucket. This
force is produced by the action of our body's muscles.
Question: Give two examples of each of the situations in which you push or pull to
change the state of motion of objects?
Answer
Examples of pushing:
(i) Player pushing a football using his foot.
(ii) Pushing an open drawer to close it.
Examples of pulling:
(i) pulling a toy car with thread to move
(ii) Opening a drawer of a table.
What causes the force to arise?
 The interaction between two objects arises from the force.

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 Force includes gravity, friction and force applied on an object in order to
move it. The force causes a change in the speed or direction of motion.
 An object will either be in motion or at rest as a result of forces. If an object is
at rest and remains at rest, the forces acting on it are said to be balanced. For it
to begin moving, we must apply additional force.
 When force is applied, two objects are involved: one that applies the force and
one that receives it.
 For example- A football placed on the ground is at rest position. For it to
move in any direction, some force should be applied to the ball. In order to
move the ball player can hit the ball.
Force arises due to interaction
 A force arises due to interaction between objects. When applying a force to an
object, the interaction between object and the source of force is required.
 For example- We can exert a force on a ball to move in any directions. It
happens when we kick the ball, so the force that arises is due to the interaction
between feet of the player and the ball.
Effects of force
Let us now look at some of the characteristics of force
1. A force can change the size and shape of an object. For example – While
playing with clay we can change the shape of clay by applying force with our
hands. The shape of rubber band changes when it is stretched.
2. A force can change the speed of a moving object. Force can slow down or
completely stop a moving object. To do this we need to apply a force in a
direction opposite to the direction of motion of the moving body.
3. A force can move an object which is at rest. For example – A stationary
trolley or trolley which is at rest can be made to move by applying some force.
So the motion of object can be halted by suitable application of force.
4. A force can change the direction of motion of a moving object. For example –
A football can changes its direction by kicking it in a different direction.
Note – Change in the mass of an object is not an effect of force.
Question: A blacksmith hammers a hot piece of iron while making a tool, How does
the force due to hammering affect the piece of iron?
Answer A blacksmith exerts muscular force when hammering a hot piece of iron. This
muscular force modifies the shape of the iron, enabling it to be shaped as needed.
Types Of Forces
There are two types of forces namely contact force and non-contact force
1. Contact forces

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These are the kinds of force that came into action when two interacting bodies are in
physical contact with each other. Muscular force and frictional force is an example of
contact force.
Types of Contact Force
a. Muscular force
 It is a type of contact force. It is the force that is exerted by the muscles of the
body.
 For example- To lift an object we use a hand. If we want to pull a bucket of
water or lift a heavy box it requires muscular force.
 Like humans, animals also use muscular force.
b. Frictional force -
 The force that causes objects to slow down and stop moving is called
frictional force. Friction always acts in the direction opposite to the direction
of motion of the object.
 For example-This is due to the force of friction when a ball comes to rest after
some time.
 This happens due to friction between the ground and the ball.
2. Non-contact forces
These are the kinds of force that is came into action when two interacting bodies are
not in physical contact with each other.
Types of Non-Contact Force
a. Magnetic force -
 Magnetic force is the force exerted by a magnet on another magnet or on a
piece of iron.
 Because a magnet is surrounded by an unseen magnetic force field, it can act
from a distance.
 For example- To separate the iron objects from the garbage since a magnet
can attract a piece of iron as the force between them is an attractive type of

force.
b. Electrostatic force –
 The force exerted by a charged body on another charged or uncharged body.

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 So, the force exerted by an electrostatic charge is referred to as an
Electrostatic Force.
 For example-Lightning. This force occurs due to electric charges. It can be
both attractive and repulsive in nature.
 It is because of electrostatic force that bits of paper move towards the comb
which was rubbed through dry hairs. This happens because when comb is
rubbed through your dry hairs it acquires a property called electric charge.
 Figure below shows Electrostatic force acting on bits of paper from a distance

c. Gravitational force –
 The force that pulls the objects towards the earth.
 It is the force of attraction between the particles of matter.
 For example – The falling of an apple from a tree.

Question: Name the forces acting on a plastic bucket containing water held above
ground level in our hand.
Answer: Muscular force and gravitational force are the forces acting on the plastic
bucket.
Magnitude Of Forces
 By term magnitude of forces, we mean the net amount of all the forces being
applied to the object. It is the sum of all forces operating on a body.
 When two forces act in the same direction, the magnitude of the force
increases. It is equal to the sum of both forces.
 When two forces act in opposite directions, the magnitude of the force
becomes less or decreases. It is the difference between the two forces.

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How can we express the force?
A force is expressed by its magnitude and direction. The magnitude of the force is a
numerical value. The direction of force is away from us when we push something and
towards us when we pull something.
Units of force
The (Standard international system of the unit ) SI unit of force is called Newton.
The unit of force is named after the renowned scientist Sir Issac Newton.
The unit of force can be defined as the force needed to accelerate a body weighing 1kg
by 1 meter per second.
F=m×a
Force Concept Map

Pressure
Pressure is defined as the force acting on a unit area of a surface. The effect of force is
measured by this quantity.
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It can be represented as
]Pressure=Force/Area
Or,
Pressure is directly proportional to force and inversly proportional to the area over
which it is applied.
So, if we decrease the amount of area, pressure increases and if we increase the
amount of area, pressure decreases.
Unit of pressure
The SI unit of pressure is Pascal.
[1Pa=1N/1m2
Applications of pressure in our daily life
 Broad Straps of shoulder bags:- The straps of shoulder bags are made
broader which increases the area of contact and reduces the pressure on the
shoulders. We know that pressure is inversely proportional to area, thus the
wider the area, the less pressure is exerted, making it easier to carry a shoulder
bag with a wide strap.
 Elephants have broader feet, which increases the area of contact with the
ground and results in lower pressure and enables the elephants to walk easily.
 It is easier to hammer a sharp iron nail than to hammer a blunt
one because the area of a sharp iron nail is smaller than that area of a blunt
nail. So, it becomes easier to hammer the nail into the wall.
 The use of skies helps to walk on snow as skies increase the area of contact
between our foot and snow. This reduces pressure on the snow.
 Peeling vegetables with a blunt knife is tough. It is much easier to peel
vegetables using a sharp knife that has sharp edges rather than a blunt knife.
This is because the sharp edge of knife has a small surface area and less force
delivers the amount of pressure needed to cut or peel vegetables.
Pressure Exerted by liquids and Gases
 It is the force exerted by liquids or gases per unit area.
 Liquids and gases exert pressure in all directions. The pressure inside a them
increase with depth.
Pressure Exerted By Liquids
 Liquids exert pressure due to the weight that liquid possesses.
 The liquid posses pressure in the downward direction.
 The pressure exerted by liquids at the bottom depends on the height of the
liquid column. The pressure exerted by liquids increases with depth.

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 For example – The body of the submarine is thick and built by strong material
because the pressure of water is high in deep-sea so to withstand that pressure
submarine is thick.
 Liquids also exert pressure in all directions on the walls of the container.
 For example – Take a container and make a hole in it. Now close the holes
with tape and fill the container with water. Then remove the tape. We will
observe that water comes out of the container in all direction.
 This shows that liquids exert pressure in all direction.
Pressure Exerted by Gases
 Gases too exert pressure on the walls of container like liquids. Air pressure
arises due to constant collisions of tiny molecules of gases present in the air
with the walls of the container it is enclosed.
 For example- When air is pumped into a bicycle tube by using a pump, the
bicycle gets inflated due to air pressure exerted by the collisions of gas
molecules in air with the inner walls of the rubber tube. For this reason,
bicycle tyres feel hard.
Atmospheric Pressure
 Atmosphere – The blanket of air that surrounds the earth is called the
atmosphere.
 All fluids (liquids and gases) exert pressure. So the air also exerts a pressure
called atmospheric pressure.
 Atmospheric pressure is the pressure within the atmosphere of Earth.
Atmospheric pressure is due to the weight of air present in the atmosphere
above us. This pressure causes air molecules to be more tightly packed
together than those that are high in the atmosphere. On the surface of the
earth, the atmospheric pressure is maximum at sea level.
 Atmospheric pressure also exists in all directions. The instrument used for the
measurement of atmospheric pressure is known as a barometer. There are
two types of barometer-
1. Mercury barometer
2. Aneroid barometer
 The mercury barometer is an ideal one as it gives the standard unit of
atmospheric pressure.
 In a mercury barometer, a column of mercury in a glass tube rises or falls the
weight of atmospheric pressure changes.
 The approximate value of atmospheric pressure on the earth’s surface is he
approximate value of atmospheric pressure on the Earth’s surface is:

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 ✅ 101.3 kilopascals (kPa) or ✅ 1 atmosphere (atm) or ✅ 760 milli meters of
mercury (mmHg) or ✅ 1.013 × 10⁵ pascals (Pa)

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🟢 🔹 What is Force? (Force kya hota hai?)
👉 Force = Push (धक्का) ya Pull (खींचना)
👉 जब दो objects interact करते हैं, तब force लगता है।
📌 Definition:
Force is a push or pull acting on an object which may change its speed, direction,
or shape.
🧠 Real Life Examples:
 Bucket उठाना (pull)
 Football kick करना (push)
 Drawer खोलना-बंद करना (pull & push)
💬 Question: Can you lift a bucket without holding it?
Answer: No! You need muscular force to pull the bucket upward.

🔹 Effects of Force (Force ke Prabhav)

Force can... Examples
Clay दबाना, Rubber band
🧊 Change shape/size
खींचना
🏃 Change speed Cycle को तेजी से चलाना
🛑 Stop a moving object Ball को पकड़ना
Ball को उलटी दिशा में
🔁 Change direction
मारना
📌 Note: Force does not change the mass of object.

🟢 🔹 Types of Force
🔸 1. Contact Forces (Jab physical contact ho)
Type Description Examples
🔹 Muscular Force Force by muscles Bag उठाना
Rubbing hands, Ball का
🔹 Frictional Force Opposes motion
रुकना
🔸 2. Non-Contact Forces (Jab contact na ho)
Type Description Examples
🔸 Gravitational Earth की खिंचाव Apple गिरना
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Type Description Examples
शक्ति
🔸 Magnetic Magnet की खिंचाव Magnet attracting iron
Comb से कागज़
🔸 Electrostatic Charged object force
attract होना

🧲 Force arises due to interaction

Example: Ball तब तक नहीं हिलती जब तक कोई उसे kick न करे – ये interaction
से ही force पैदा होता है।

🔹 Magnitude of Force (Bal ki Taaqat)

📌 Same direction → Add the forces
📌 Opposite direction → Subtract the forces

 Ram pulls 20N, Shyam pulls 30N → same direction ⇒ Total = 50N
🧠 Example:

 If opposite direction ⇒ Net = 10N

🔹 How to express Force?

 Magnitude (Amount)
 Direction (किधर लगाया)
📐 SI Unit = Newton (N)
📌 Formula: F = m × a (Force = Mass × Acceleration)

🟡 🔹 Pressure (दबाव)
📌 Definition:
Pressure = Force / Area
📍 More area = Less pressure
📍 Less area = More pressure
🧠 Real-Life Examples:
 Wide straps = कम दबाव (कंधे पर बैग आराम से टिका)

 Elephants के पैर = ज़्यादा area ⇒ कम दबाव ⇒ easily walk on mud

 Sharp knife = ज़्यादा दबाव (cutting easy)

🔹 Unit of Pressure
🧪 SI Unit: Pascal (Pa)
1 Pascal = 1N / 1m²

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🟣 🔹 Pressure by Liquids & Gases
🔸 Liquids:
📌 Pressure = Due to weight of liquid
📌 Increases with depth
🧠 Example:
 Submarine का body strong होता है क्योंकि गहराई में पानी का

 Holes in bottle से हर दिशा में पानी निकलता है ⇒ liquids exert pressure

pressure ज़्यादा होता है

in all directions
🔸 Gases:
📌 Molecules की टक्कर से gas pressure होता है
📌 Example:
 Tyre inflate करना
 Balloon फटना – ज़्यादा pressure से

🔵 🔹 Atmospheric Pressure (वायुमंडलीय दबाव)

📌 Air का weight हम पर pressure डालता है
📌 ज़मीन के पास pressure ज्यादा होता है
📌 Measured by: Barometer (Mercury or Aneroid)
🧪 Approximate Value:
✔️1 atm = 101.3 kPa = 760 mmHg = 1.013×10⁵ Pa

 Suction cup दीवार से चिपक जाती है ⇒ Atmospheric pressure helps hold

🧠 Real-life connect:

it

✅ One-Liner Competitive Q&A

❓ Question ✅ Answer
Force = Push or ____? Pull
SI Unit of Force? Newton
SI Unit of Pressure? Pascal
More area = ____ pressure? Less
Force without contact = ? Non-contact force
Which force slows moving object? Friction
Force acting per unit area? Pressure
Instrument to measure air pressure? Barometer

📊 Concept Map (Summary at a Glance)

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🔚 Conclusion: Why this chapter matters?

 समझ में आता है कि पुश-पुल से movement कैसे होता है
 Engineering, construction, space, sports, daily life – हर जगह force और
pressure use होता है!

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Chapter 2 Friction
Meaning of friction
 When two objects with their surfaces in contact rub against each other, they
cause friction.

 Friction is the force opposite to the direction of motion.

 Friction is the force that acts when one object tries to move or slide over the
surface of another object.
 It can be defined as the resistance of motion when one objects rub against other.
 Friction works against the motion and acts in the opposite direction. However,
friction does not always oppose the motion, it also helps in motion.
 The S.I unit in which frictional force is measured is, Newton.
 Examples of friction
1. Friction between the tyres of vehicles and the road.
2. To make the box move, we have to apply a force to overcome the force of
friction.
3. Friction between pen and book.
What is Friction?The force, which opposes the relative motion between two surfaces
in contact is known as friction. It occurs due to surface irregularities of the two objects
in contact.
What is Surface Irregularities?This unevenness of the surface is called surface
irregularities or roughness.

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What are the examples of friction?
1. Writing on paper using a pencil: Friction between the graphite in a pencil and a
sheet of paper leaves a mark on the paper.
2. Warming hands in winter: As friction produces heat you can warm your hands in
winter by rubbing them against each other. So heat from friction can be useful.
3. Gymnasts apply some coarse substances on their hands to increase friction for better
grip.
Cause of friction
 The root cause of friction is the irregularities or rough edges that is ridges and
grooves present on the two surfaces which are in contact. Due to this they get
interlocked with each other and cause friction.
 Even smooth surfaces like tiles in houses, office, school have a large number
of irregularities when seen under a microscope.
Why is it difficult to walk on a smooth or wet floor?
Due to less friction between our foot and floor. As the interlocked irregularities
possess a layer of water which decreases friction.
What Causes Friction?
Friction exists between two surfaces due to abnormalities on the surfaces of the
objects in contact, as well as the interlocking of the two surfaces' micro-level
imperfections. So, this force is caused by molecular adhesion, surface roughness,
ploughing effect and deformations.
Factors affecting friction
The force of friction depends on the following factors
 It acts in a direction opposite to the direction of motion.
 It depends on the mass of the body
 It depends on the surface's nature, as smooth surfaces have fewer irregularities
and thus less friction. As a result, moving an object to a smooth surface is
easier than moving an object to a rough surface.
Which one is easier to hold in hand: an earthen pot or a glass tumbler. Why?
Because of the smoother surface, the glass tumbler creates less friction and it is not
easier to hold. On the other hand, an earthen pot has a rougher surface which creates
more friction and thus makes it easier to grip.
Spring Balance

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Spring balance is a device used for measuring the force (or weight) acting on an
object.
Christian Huygens, invented the first balance springs. Spring balance measures the
weight. Spring balances are used commercially.
Working of spring balance
Spring balance consists of a coiled spring that gets stretched when a force is applied to
it. Stretching of the spring is measured by a pointer moving on a graduated scale. The
reading on the scale gives the magnitude of force or weight of the object.

Types of friction
There are four types of friction namely
1.Static friction
2.Rolling friction
3.Sliding friction
4.Fluid friction
1. Static friction
 The word static means at rest.
 Static friction can be defined as the friction that acts when we try to move an
object at rest or the object which is not moving. It is the strongest type of
friction.
 For example –
o Cup placed on a table
o Scenery hanging on a wall
o A car parked on a hill.
 Limiting friction is the friction acting on a body when it is about to start
moving.
2. Sliding friction
 Sliding friction is smaller than static friction as a smaller force is now required
to keep the object moving.

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 Sliding friction can be defined as the friction that acts when two surfaces slide
over each other. If the applied force exceeds the limiting friction the
irregularities on it do not get interlocked on the surface on which it is moving.
3.Rolling friction
 Rolling friction is always less than sliding friction as rolling reduces friction.
Rolling friction is the weakest type of friction.
 Rolling friction can be defined as the force that opposes the motion when an
object rolls over another object.
 For example –
o Ball bearings
o Skateboards.

What are the benefits of using ball bearings?

Due to the fact that rolling friction is less than sliding friction, ball bearings assist in
maintaining the smallest possible surface of contact between two moving surfaces.
4. Fluid friction
 The above three friction occur between solid surfaces whereas fluid friction
occurs in fluids, that is in liquids or gases. A fluid is a substance that can flow
and take the shape of a container.
 Fluid friction can be defined as the friction that occurs when objects move
across fluids. Another name for fluid friction is a drag. It resists the movement
of viscous fluids relative to each other.
 The force exerted by fluids is called drag. Drag force acts in a direction
opposite to the direction of motion of the object. For example - When an
aeroplane moves at a high speed it experienced air resistance.
 Fluid friction depends on the following factors
1. speed of the object with respect to the fluid.
2. the shape of the object.
3. size of the object.
4. nature of the fluid.
Ways to reduce fluid friction
 Firstly the question arises that why there is a need to reduce fluid friction.
 As when objects move through fluids, they lose some of their energy in
overcoming the fluid friction which decreases the efficiency of an object. To
overcome this there is a need to reduce fluid friction.
 Fluid friction can be reduced by moulding the shape of an object which offers
little resistance to fluids. The streamlined shape is best suited for objects that

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move in air or water. The streamlined shape is like a thin wedge that cut the
air or water and moves forwards.
 For example – An aeroplane has a special shape called streamlined shape to
reduce friction offered by air. Similarly, boats, birds and fishes have this
special and suitable shape to reduce fluid friction and avoid loss of energy.

What are the types of friction?

The four types of friction are static, sliding, rolling and fluid frictions.
What is fluid friction?
Fluid friction is the frictional force exerted by fluids i.e., liquids and gases.
Friction - A necessary evil
Friction is called a necessary evil as friction has its advantages as well as
disadvantages also.
On the soles of shoes, the grooves are present. Grooved soles provide increased
friction to the ground, resulting in a greater grip when walking. Because the earth has
friction, we can walk easily. As a result, friction is required even in simple tasks such
as walking.
Moving on a wet muddy route or a damp marble floor is a challenging chore. This is
due to the fact that these surfaces provide relatively little friction to a person's feet.
Advantages of friction
 Friction helps in the generation of heat.
 Friction helps in stopping bicycle or any vehicle by applying brakes.
 Nails can be fixed in a wall due to friction
 Friction helps to write, walk.
 Jumping out of an aeroplane with a parachute.
 Ignition of matchsticks.
 The motion of pistons.
 Provide support to the ladder against the wall.
Disadvantages of friction
 Friction produces heat which may damage machines and cause the wastage of
energy.

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 Friction results in the wear and tear of objects, for example, the moving parts
of a machine, the tyres of a car, the soles of shoes, and so on.
 Friction resists motion
 The cause of forest fires is the friction between tree branches.
 Production of noise in machines due to friction.
 Consumption of more fuel in vehicles.
Ways to reduce friction
 Use of lubricants (Substances like oil or grease polish on the surface of
machines to reduce friction and the process of applying lubricants to machines
is known as lubrication)
 The use of wheels also helps to reduce friction.
 The streamlined body of an object can reduce friction.
 The use of ball bearings between machine parts greatly helps to reduce
friction as rolling friction is less than sliding friction.
 Sprinkling powder on dholak can reduce friction.
 Polishing surfaces that come into contact with one another to way to reduce
friction. Polishing the surface eliminates imperfections and thereby smooths
the surface.
What is lubrication?
Lubricants are substances like oil and grease etc. They help to reduce friction by
forming a thin film between the different parts of a machine.
Ways to increase friction
Under some circumstances, there is a need to increase friction
 Make surfaces rougher- The roughness of the surfaces in contact can be
enhanced to increase friction.
 By increasing the mass of the object that is moving.
 The treads(A series of patterns )present on the tyres of car, buses and trucks
help to increase friction
 The grooves on the sole of shoes help to increase friction and provide better
grip to the ground.
 The brake shoes in automobiles are used to increase friction.
Why are brake pads used in the brake system of automobiles and cycles?
Brake pads are used to improve friction, allowing the brake to operate more
effectively. When we drive the car, the pads do not make contact with the wheels, but
when we press the brake lever, the pads interrupt the rim's motion due to friction, and
the wheels come to a halt.
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🔹 What is Friction? (Friction kya hota hai?)

👉 जब दो surfaces आपस में contact में होती हैं और एक दूसरे पर rub करती
हैं, तो एक resistance पैदा होता है – इसी resistance को कहते हैं Friction
(घर्षण)।
📌 Definition:
Friction is a force that opposes the motion of an object when it slides, rolls, or
moves over another object.

🧠 Quick Real Life Examples:

Situation Friction का Role
Paper और graphite के बीच
Pencil से writing
friction
Rubbing hands Heat generation due to friction
Tyres on road Helps in grip and movement
Dholak पर powder
Friction कम करने के लिए
डालना

🔸 Friction acts in opposite direction

यानि अगर कोई object right जा रहा है, तो friction उसे left से oppose करेगा।

🧲 Cause of Friction:
🔹 Surface Irregularities (Tiny ridges and bumps)

🔹 ये roughness आपस में interlock होती हैं ⇒ Friction पैदा होता है

🔹 Even smooth दिखने वाली surfaces भी microscopic level पर rough होती हैं

📌 इसलिए wet floor या ice पर चलना मुश्किल होता है – वहाँ कम friction होता
है।

🔹 Factors Affecting Friction:

Surface roughness ज्यादा rough ⇒ ज्यादा friction

Factor Impact

Weight of object ज्यादा weight ⇒ ज्यादा friction

कुछ surfaces naturally ज्यादा friction
Nature of material

ज्यादा दबाव ⇒ ज्यादा interlocking

देती हैं
Contact force

By Adarsh 18
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⇒ ज्यादा friction
Factor Impact

🔺 Types of Friction:
Type Description Example
🔸 Static जब object rest में हो Cup on table
🔸 Sliding Object slides Box being pushed
🔸 Rolling Object rolls Wheels, ball bearings
🔸 Fluid Object moves in liquid/gas Fish in water, Aeroplane in air
📌 Friction order (Strongest → Weakest):
Static > Sliding > Rolling > Fluid
🔹 Why Ball Bearings are used?
✅ Sliding friction को rolling में बदलने के लिए
✅ Efficiency बढ़ाने के लिए
🟢 Friction - A Necessary Evil
📌 Friction has both advantages & disadvantages, इसलिए इसे “necessary evil” कहा
जाता है।
✅ Advantages of Friction:
 Walk karna possible बनाता है
 Pen से लिखना possible बनाता है
 Matchstick ignite करती है
 Heat produce करता है (rubbing hands in winter)
 Car, cycle brakes friction से ही काम करते हैं
 Climbing, gripping, jumping में मदद करता है
❌ Disadvantages of Friction:
 Wear & tear of tyres, machines
 Machines में heat produce करके energy waste करता है
 Forest fires due to branch rubbing
 Vehicles consume more fuel
 Noise in machines
🔧 How to Reduce Friction?
तरीका Explanation
Lubricants Oil, grease, etc. form smooth film
Surface smooth करने से friction कम
Polishing
होता है
Ball bearings Sliding को rolling में बदलते हैं
Streamlined shapes Fish, birds, airplanes – कम drag
By Adarsh 19
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तरीका Explanation

Dholak, carrom board में use होता

Powder
है

🔺 How to Increase Friction?

Method Example

भारी object ⇒ ज्यादा friction

Surface rough बनाना Tyre treads, rough shoes
Mass बढ़ाना
Grooves in tyres/shoes Better grip
Brake lagane पर ज्यादा friction
Brake pads
पैदा करते हैं

✅ Glass – smooth ⇒ कम friction ⇒ difficult to grip

❓ Why is it difficult to hold a glass tumbler than an earthen pot?

✅ Earthen pot – rough ⇒ ज्यादा friction ⇒ better grip

🧪 Spring Balance kya hota hai?

📌 Based on: Hooke’s Law – ज्यादा force ⇒ spring ज्यादा stretch होता है
✅ Spring balance एक device है जो force या weight को measure करता है।

📌 Unit: Newton (N)

🟣 Fluid Friction (Drag)
📌 Fluids = Liquids + Gases
📌 Moving object पर fluid एक opposite force लगाता है जिसे कहते हैं Drag

 Plane हवा में चलता है ⇒ Air resistance

🧠 Examples:

 Boat पानी में चलती है ⇒ Water drag

📌 Factors affecting fluid friction:
 Speed
 Shape
 Size

✅ Streamlined bodies (जैसे fish, birds, airplanes) ⇒ कम drag ⇒ high efficiency

 Nature of fluid

🔄 Competitive Quick Questions:

Question Answer
Friction opposes ______? Motion

By Adarsh 20
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Question Answer
SI unit of friction? Newton
Weakest friction type? Rolling
Which shape reduces fluid friction? Streamlined
What increases grip on shoes? Grooves
What reduces wear and tear in machines? Lubricants
Who invented spring balance? Christian Huygens
Friction – good or bad? Both – Necessary Evil

🔚 Concept Map:

कुछ न समझ आये तो पूछ लेना 9455857477

By Adarsh 21
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Chapter 3 Sound
Introduction to Sound
 Sound is a form of energy that travels in the form of vibrations through the air
or any another medium.
 Vibration is defined as a rapid to and fro or up and down movement about a
mean position.
 Vibrations travel through a medium such as air and reach our ears where they
are interpreted by the brain as sound.
 Human beings are capable of producing sound which originates from the
larynx or the voice box in the neck. The sound produced is controlled by thin
membranous structures known as vocal cords that stretch across the larynx.
 The vibrating body can be- a stretched animal hide (as in drums and table),
stretched strings (as in guitar and sitar), or air columns (as in flute or pipes).
Sound is produced by a vibrating body. In other words, any vibrating body would
always produce sound. Sometimes, the vibration is clearly visible and the sound is
strong, whereas in some cases, the vibration is small and the sound is feeble. (Note :
The to and fro or back and forth motion of a body is termed as vibration or
oscillatory motion). When the diaphragm of a drum is struck, it vibrates and produces
sound. When the strings in a violin vibrates, it produces sound. When the air column
vibrates within a flute, it produces sound. As seen, different parts of the musical
instruments (diaphragm of the drum, strings of violin, air column within in flute)
vibrate to produce sound.
The voice Box
In humans also, sound is produced because of the vibration of his voice box also
known as larynx. The Larynx is situated at the upper end of windpipe. It comprises
of 2 stretched membranes called vocal cords with a narrow slit between them. When
we talk, air passes through those stretched membranes they produce different
of sounds in accordance with the stretching

By Adarsh 22
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Sound needs medium for propagation
Sound can propagate through solids, liquids and gases. In fact, it needs a medium to
propagate, be it solid, liquid or gases. It cannot propagate through vacuum.
Sound can propagate through Solids: The doctor checks us using the stethoscope.
He can hear the sound from within our body because sound travels through solids

Sound can propagate through liquids: In fact, this is how aquatic animals
communicate with each other.

Sound can propagate through gases/air: This is the reason why we are able to hear
a person standing near us speak.

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Human Ear
The shape of our outer ear is like a funnel. Sound waves enters inside. It travels down
a canal and at the end of it, touches a thin stretched membrane called the eardrum.
The eardrum vibrates to the effect of the sound. The ear passes on these vibrations to
the inner ear and then there to the brain, which processes it. That is how we hear.!

To understand better, take a toy drum. Bang on diaphragm with various intensity
blows. First strike gently with your hands. Then blow slightly harder with the cords.
Then very hard on so. In all the cases, see the diaphragm vibrates according to the
intensity of the blow and then it produces the sound. This is analogous to the ear.
Characteristics of Sound
Sound is characterized by 2 important features
 Frequency
 Amplitude

By Adarsh 24
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1. Frequency : The number of oscillations per second is called the frequency of

oscillation. Frequency is expressed in hertz. Its symbol is Hz.
Frequency = No of oscillations
Time (in seconds)
If pendulum oscillates 15 times in one minute, the frequency is given by
Frequency = No of oscillations = 15 = 0.5 Hz
Time (in seconds) 30
Frequency determines the shrillness or the pitch of the sound. Higher the
frequency, higher the pitch or it is said that the sound is shrilling. Lower the
frequency, lower the shrill or pitch. Eg: Babies voice has more frequency and
thereby more shrilling than an adult voice.
2. Amplitude: Amplitude is a measure of the intensity of the sound. Amplitude
determines the Loudness of sound. Loudness is proportional to the square of
the amplitude of the vibration body producing sound
Loudness = k.(Amplitude)2 (where k is the proportionality constant)
The loudness is expressed in a unit called decibel (dB).

The more the amplitude of vibration, the sound is the loud. The lesser the
amplitude of vibration, the sound is feeble.
Audible & Inaudible Sound
 The human ear can detect sounds in the range of 20Hz-20KHz. These are
called Audible Sounds. Eg: Music, Instruments, Crackers.
 Frequencies below 20Hz and greater than 20KHz cannot be heard by the
human ear. These are called Inaudible Sounds. Eg: It is believed that bat calls
are in the inaudible ultrasonics range. Dogs can hear frequencies greater than

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20KHz, so they are used by the police to respond to such whistles. Ultrasound
scans produce sounds in this range.
Noise & Music
 Music refers to pleasant sounds which we would like to hear. Eg: Musical
instruments like flute, guitar, violin etc. Your favourite singer singing a
melodious song.
 Sounds which are unpleasant to hear are termed as noise. Eg : Honking of
vehicles,Loucrackers, Explosions

Noise Pollution
Presence of excessive or unwanted sounds in the environment around us is called
as Noise Pollution.
Sources of Noise Pollution
 Vehicles honking on the road and traffic signals
 Explosions
 Bursting crackers
 Huge machines at construction sites, factories
 Loud Speakers
 TV, Music system played at high volumes
 Some kitchen and home appliances like mixers, ACs etc

Harm of noise pollution

Noise pollution mostly leads to health related problems such as
 Anxiety, Stress

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 Hypertension (High BP)
 Lack of sleep
 Prolonged exposure can lead to temporary or even permanent hearing
impairment

Measure to limit Noise Pollution

 Industry and factory units which produce a lot of noise should be setup away
from residential areas.
 Silencers (Silencing devices) should be installed in air crafts, industry and
home appliances which tend to produce a lot of noise.
 A lot of trees should be built around such factory units so that they absorb
sound and protect the residential areas around them from the loud noise.
 Minimal use of horns in vehicles. No honking.
 Low volume for TV, music systems at home.
 Avoid or minimize use of crackers.

अब इसका SUMMARY HINGLISH मे देता हूँ रटना मत कुछ समझ न आए तो पूछ

लेना|
What is Sound?
🔸 Sound ek energy ka form hai jo vibrations ke through air, liquid ya solid medium
mein travel karta hai.
🔸 Jab koi object vibrate karta hai, toh woh sound produce karta hai.
🔸 Vibration = To & Fro motion (आगे-पीछे हिलना)
🎤 Example:
 Drum bajane par uski diaphragm vibrate karti hai
 Guitar mein string vibrate hoti hai
 Flute mein hawa ka column vibrate karta hai

By Adarsh 27
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🧠 Human Sound Production: Voice Box (Larynx)

 Larynx neck ke andar hota hai.
 Vocal cords ke vibration se sound produce hota hai.
 Air jab vocal cords ke beech se guzarti hai, toh woh vibrate karke sound
banata hai.

🚨 Important Concept (Competitive!)

Q: Sound kis medium mein travel kar sakta hai?
✅ Solid (e.g., stethoscope)
✅ Liquid (e.g., dolphin sounds in water)
✅ Gas (e.g., human speech in air)
❌ Vacuum mein sound travel nahi karta (No molecules, no vibration transfer)

👂 Human Ear Working

 Outer ear = Funnel shape
 Sound waves → Ear canal → Eardrum vibrates → Inner ear → Brain
 Analogy: Drum ke membrane ki tarah eardrum vibrate karta hai.

🎼 Characteristics of Sound
1. Frequency (Hz):
o No. of vibrations per second.
o Jyada frequency → shrill (teekhi aawaz)
👉 Baby ki aawaz > Adult voice
o Audible range = 20 Hz to 20,000 Hz (20 kHz)
2. Amplitude:
o Vibrations ki intensity.

o Loudness ∝ Amplitude²
o Zyada amplitude → loud sound.

o Unit: Decibel (dB)

🎧 Types of Sound
Heard by
Type Frequency Range
Humans?
Audible 20 Hz – 20 kHz ✅ Yes
<20 Hz (infrasound), >20 kHz
Inaudible ❌ No
(ultrasound)

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Heard by
Type Frequency Range
Humans?
🦇 Bats & 🐶 Dogs use ultrasonic
sounds!

🎶 Music vs Noise
Music Noise
Pleasant sound (violin, song) Unpleasant (honking, crackers)
Regular pattern Irregular and harsh

🔊 Noise Pollution
❗ Unwanted or excessive sound in environment
🎯 Sources:
 Honking vehicles
 Factories
 Loudspeakers
 Crackers
 Kitchen appliances
⚠️Harms of Noise Pollution
 Anxiety
 High Blood Pressure
 Hearing loss
 Sleeplessness
✅ Measures to Control Noise Pollution
 Factories away from homes
 Use of silencers in vehicles & machines
 Tree plantation around noisy areas
 Use low volume TV/music
 Crackers ka limited use
 No honking zones

🎯 Competitive Style Questions (Practice)

1. Q: What is the unit of frequency?
A: Hertz (Hz)
2. Q: What is the audible range of humans?
A: 20 Hz to 20,000 Hz
3. Q: Which part of the ear vibrates when sound reaches it?
A: Eardrum
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4. Q: Why can’t sound travel through vacuum?
A: Vacuum mein koi particles nahi hote, isliye vibrations transfer nahi hoti.
5. Q: Loudness is proportional to?
A: Square of amplitude
6. Q: What is ultrasound used for in medicine?
A: Internal body scan (Sonography)

📚 Trick to Remember:
F-A-L
 Frequency → Pitch
 Amplitude → Loudness
 Larynx → Sound production in humans

कुछ न समझ आये तो पूछ लेना

9455857477

By Adarsh 30
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Chapter 4 Light
Introduction to Reflection
 The balancing of light from a surface is called reflection. Or
 The to and fro movement of light in the same medium after striking an opaque
surface is called reflection.
 The amount of light that is reflected depends on the material and nature of the
surface on which light falls
 An opaque body absorbs some of the light that falls on it and reflects the
remaining light.
 A transparent body allows almost all the light to pass through it and reflects
very little light.
 A smooth and a highly polished surface such as a shiny stainless steel surface
or a mirror reflect almost all the light that falls on it.
No light, No sight
 We see objects around us due to 2 factors (i) Eyes (ii) Light.

 With eyes and no light, (as in night), we cannot see objects around us.
Similarly, if there was light and an individual is visually impaired, he/she still
cannot see. Therefore, we need both factors ie Eyes and Light to see objects
around us.
Reflection of light on a plane surface
 A plane polished surface capable of regularly reflecting almost all the light
falling on it is known as a plane mirror.
 A ray of light which falls on the mirror is called incident ray.
 The ray which is sent back to the original medium is called the reflected ray.
 The perpendicular to the reflecting surface at the point of incidence is called
the normal.
 The angle made by the incident ray with the normal of the point of incidence
is called the angle of incidence.
 The angle made by the reflected ray with the normal at the point of reflection
is called angle of reflection.
Laws of Reflection
When reflection takes place, it follows certain rules which are known as the laws of
reflection.
The laws followed during reflection are as follows-
By Adarsh 31
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First law
The incident ray reflected ray and the normal at the point of incidence lie in the same
plane.
Second law
The angle of incidence is always equal to angle of reflection, that is
<i = <r

Formation of image by a plane mirror

 The characteristics of image formed could vary depending on the type of

mirror used.
 The characteristics of an image formed by plane mirror are as follows-
 The image formed is erect.
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 The image is of same size as the object.
 The image is laterally inverted, that is, the right appears as the left side of the
image.
 The image is as far behind the mirror as the object is in front of it.
 The image formed is virtual, that is, it cannot be caught on a screen
Regular and diffused Reflection
Reflection of light is of two kinds depending on the nature of the reflection and
diffused or irregular reflection.

Regular reflection
When the reflecting surface is very well polished and smooth, the light that falls on it
is evenly reflected in only one direction. This phenomenon is known as regular
reflection.

Diffused reflection
If the reflecting surface is irregular, the ray of light that falls on it are scattered in all
directions. This is called irregular or diffused reflection.

Multiple reflections
Take two plane mirrors and place them such that they make an angle between them.
Place an object between the mirrors. You can see several images in both the mirror.
This is because the image formed by one mirror act as the object for the second
mirror. This phenomenon is referred to as multiple reflections.
The number of image formed depends on the angle between the mirrors.
The number of images formed is found using the formula.
n = (360/O) -1
n = number of images
By Adarsh 33
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o = angle between the two mirrors.
Image formation at angled Mirrors
When two mirrors are placed a various angles w.r.t each other, the light gets reflected
over and over again it forms, multiple images.

Let M1 and M2 be 2 mirrors. Object O is the object.

If of angle between the mirrors is 90 degrees : Three images are formed. (Case i)
 Image I1 of Object O due to Mirror M1 is formed
 Image I2 of Object O due to Mirror M2 is formed
 Now Object is I2 and I1. The image of I1 is formed at position I3 due to
mirror M1. The image of I2 is formed at position I3 due to mirror M2.
If the angle between the mirrors is 0 degrees ie mirrors being parallel to each
other: Infinite images are formed.(Case ii)
 Image I1 of Object O due to Mirror M1 is formed
 Image I2 of Object O due to Mirror M2 is formed
 Now Object is I2 and I1. The image of I1 is formed at position I3 due to
mirror M2. The image of I2 is formed at position I4 due to mirror M1.
 Now Object is I3 and I4. The image of I3 is formed at position I5 due to
mirror M2. The image of I4 is formed at position I6 due to mirror M1. And it
continues...
Going by this, as the angle decreases from 90 to 0, the number of images keeps
increasing. Recall the case of a Kaleidoscope wherein the angle between the mirrors
is 60 degrees. So, many images(>3, 3 images are formed for 90 degrees) are formed.

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Periscope: Periscope is an example wherein mirrors are placed at 45 degrees w.r.t
each other.

 The light from the object is incident on the mirror M1 at an angle of 45

degrees.
 The light is reflected away from the mirror M1 at an angle of 45 degrees.
 It is again incident on mirror M2 at the same angle 45 degrees.
 Mirror M2 reflects it back to your eye at the same angle.
Periscopes are commonly used in submarines and military mainly for spying that is
for observation from concealed positions. For a submarine which is deep inside the
water, the surface and the objects above cannot be seen otherwise. But, by fitting a
periscope, objects on the surface and outside can be viewed inside the submarine
Instrument Based on Multiple reflection
Kaleidoscope
 This instrument works on the principle of multiple reflections. It consists of
three plane mirrors inclined at an angle of 60° to each other.
 The arrangement is kept in a cylindrical cardboard base with a few pieces of
coloured glass at one end.
 The mirrors form multiple images of these glass pieces, resulting in beautiful
pattern when seen from the other end.
 On rotating the cylindrical box, the pattern change continuously as the
position of glass piece shifts.
Periscope
 It is another instrument which uses the principle of multiple reflections.
 This instrument also needs two plane mirrors that are placed at an angle of 45°
to the vertical.
 In a periscope mirrors are placed at a distance from each other.
 The image formed by one mirror acts as the object for the other mirror.
 The main use of Periscope is in submarines that remain under water.
Refraction of Light
 The change of direction of light rays when they pass from one optical medium
into another is called refraction of light.

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 A transparent substance is called optical medium.
 There are certain rules that are followed by light during refraction.
 When light travels from a rarer (eg. Air) to a denser (eg. Glass) medium it
bends towards the normal.
 When light travels from a denser to a rarer medium, it bends away from the
normal.
 When light travel along the normal there is no deviation that is the ray suffers
no refraction.
Refraction of light through a Prism
A prism is a transparent solid body, often having triangular bases. When three
rectangular surface that it forms two triangular faces at opposite ends, they form
prism. The triangular faces are called the principal faces of the prism.
Dispersion
 The splitting up of light into its constituent colours is called dispersion.
Sunlight is a mixture of light of several colours. It is known as white light.
When white light passes through a prism, dispersion takes place because rays
of different colours are deviated through different angles by a prism. Violet is
deviated the most and red the least.
 The band of colours obtain because of dispersion of light is called a spectrum.
 The spectrum of sunlight consists of violet, indigo, blue, green, yellow,
orange and red.
Rainbow
 The rainbow is a very beautiful natural spectrum on a large scale. It is formed
in the direction opposite to the sun.
 When there is moisture in the air the tiny droplets of water acts as prisms and
disperse sunlight.

Human Eye
 The eye is natural optical instrument that forms an image of objects on a
screen called the retina. This enables us to see to objects.

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 The front part of the eye is called the cornea and is made up of a transparent
material.
 ;Behind the cornea is the iris the coloured parts of the eye.
 ;In the middle of the iris is a hole called the pupil. It appears black because no
light is reflected from it.
 The iris adjusts the amount of light entering the eye through pupil.
 Behind the iris is a convex lens. The eye lens is held in position by a pair of
muscles called ciliary muscles.
 The lens forms an Image of an object on the retina which is at the back of the
eye.
 The retina is covered by a large number of nerve cells sensitive to light which
carry the impression to the brain by means of optic nerve.
 There are two kinds of nerve cells on retina-
 Cones – that sense colour & are sensitive to bright light.
 ;Rods – which are sensitive to dim light
Power of accommodation of Eye
 The ciliary muscles alter the thickness of the lens enabling the eye to see far
and near objects equally clearly.
 The ability of eye to adjust itself to see objects at different distances clearly is
called the power of accommodation of the eye.
 The least distance at which eye can clearly see an object is called the near
point or the least distance of distinct vision.
 The far point of the eye is the maximum distance to which the eye can see.
For a normal eye it is at infinity.

The blind spot

here is one point on the retina where the nerve fibers enter the optic nerve. The image
falling on this part of the retina cannot be seen and hence it is known as the blind spot.
Persistence of Vision
To see and object, its image must be formed on the retina by the eye lens. As soon as
the object is removed, the image disappears but the brain remembers the image for
1/10th of a second even after the removal of object. This effect is called Persistence of
vision.
Defects of vision and their correctionThe two common \defects of the eye are short-
sightedness or myopia, and long – sightedness or hyper- metropia or hyperopic.
Myopia (Short – sightedness)

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 Myopia is a defect of the eye in which distant objects cannot be seen clearly
but nearby objects can be seen clearly.
 To correct this defect, a diverging or concave lens is used to create an extra
divergence so that the images get formed on the retina.
Hypermetropia (Long- sightedness)
 Hypermetropia is a defect of the eye in which distant objects can be seen
clearly by the eye but nearby objects cannot be seen distinctly.
 This defect is because the focal length of the eye lens too long or the eyeball
is too short. As a result, nearby objects are brought to focus at a point behind
the retina.
 The defect of Hypermatropia may be corrected by using a converse or
converging lens since the rays require an extra convergence to meet at a lesser
distance.
Cataract
 This is another defect of the eye generally occurring at old eye. In a person
suffering from cataract, the eye lens becomes cloudy leading to loss of vision.
 Cataract can be treated by surgically removing the eye lens and inserting in
its place a new artificial lens.
Braille

 The Braille system is a method of writing for the blind.

 It uses six raised dots. The positions of different dots represent the different
letters of the alphabet.
 Visually challenged people can read them by feeling them with their fingers.
The method was developed by Louis Braille of Paris.
Eye care

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 A diet rich in Vitamin A, selenium and vitamin C and E help to maintain good
eyesight and to prevent to delay development of cataract.
 Do not read in very dim or very bright light; avoid reading in a moving
vehicle.
 Avoid watching TV or working on a computer for long sessions.
अब इसका SUMMARY HINGLISH मे देता हूँ रटना मत कुछ समझ न आए तो
पूछ लेना|
🌟 Introduction to Light
 Light is a form of energy that enables us to see.
 Without light or eyes, we cannot see — both are equally important.
 Light always travels in a straight line.
 Speed of light ≈ 3 × 10⁸ m/s in vacuum.

🔍 Reflection of Light
📌 Definition:
"जब light किसी surface से टकराकर वापस उसी medium में लौटती है, उसे
reflection कहते हैं।"
🔁 Types of Reflection:
Type Description Example
Regular Reflection Smooth surface → light reflects uniformly Mirror, Steel Plate
Rough surface → light scatters in all
Diffused Reflection Wall, Paper
directions
🔍 Terms in Reflection:
 Incident Ray → Light that hits the surface.
 Reflected Ray → Light that bounces back.

 ∠i = ∠r → Angle of incidence = Angle of reflection.

 Normal → Perpendicular line at point of incidence.

🎯 Laws of Reflection (Competitive Focus):

2. ∠i = ∠r (Very important for MCQs & reasoning)

1. Incident Ray, Reflected Ray, and Normal lie on the same plane.

🔭 Plane Mirror & Image Formation

Feature Description
Erect or Inverted Erect
Size Same as object
Real/Virtual Virtual (cannot be taken on screen)
Lateral Inversion Yes (Left appears Right)

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Feature Description
Distance As far behind as object is in front

🧠 Multiple Reflections & Formula

If 2 mirrors are at angle θ:
n=360θ−1n = \frac{360}{θ} - 1n=θ360−1
👉 For θ = 90°, images = 3
👉 For θ = 60°, images = 5
👉 For θ = 0°, infinite images (Parallel mirrors)

🧪 Kaleidoscope & Periscope (Application based)

 Kaleidoscope: Works on multiple reflections → used in toys/designs.
 Periscope: Uses two mirrors at 45° → Used in submarines.

💡 Refraction of Light
📌 Definition:
"जब light एक medium से दूसरे medium में जाती है और दिशा बदलती है, उसे
refraction कहते हैं।"
🔁 Rules of Refraction:
Medium Change Light Bends
Rarer → Denser Towards normal
Denser → Rarer Away from normal
Along Normal No bending
🧪 Application: Coin in water appears raised, pencil looks bent in glass.

🌈 Dispersion & Spectrum

 Dispersion: White light splits into 7 colours (VIBGYOR).
 Prism causes dispersion.
 Red bends least, Violet bends most.
 Rainbow is a natural dispersion due to sunlight + water droplets.

👁 Human Eye: Natural Optical Instrument

📌 Parts of Eye:
Part Function
Cornea Transparent front portion
Iris Controls amount of light entering
Pupil Appears black; allows light in
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Part Function
Lens Focuses image on retina
Retina Light-sensitive layer (has rods/cones)
Optic Nerve Sends image info to brain
🔹 Image is formed inverted & real on retina, brain flips it.

🎯 Important Terms:
 Persistence of Vision: Brain retains image for 1/10 second.
 Blind Spot: No image detection due to absence of nerve cells.
 Accommodation: Ability of eye lens to focus near and far.
 Near Point: 25 cm (for normal eye)
 Far Point: Infinity (for normal eye)

🔎 Defects of Vision & Correction

Defect Problem Lens used
Myopia Near clear, far blurred Concave lens
Hypermetropia Far clear, near blurred Convex lens
Cataract Cloudy lens Surgery required

♿ Braille System
 Writing method for visually impaired.
 Raised dots system developed by Louis Braille.
 Can be read by touch.

✅ Competitive Focus (Q/A Style):

o A: ∠i = ∠r (2nd Law of Reflection)

1. Q: Which rule determines angle of reflection?

2. Q: What causes lateral inversion?

o A: Plane mirror reflects left to right.
3. Q: Why does coin appear raised in water?
o A: Due to refraction.
4. Q: Which lens is used to correct Myopia?
o A: Concave lens.
5. Q: Why rainbow appears opposite to sun?
o A: Sunlight undergoes dispersion in water droplets.
6. Q: What is power of accommodation?
o A: Eye's ability to focus near & far objects.
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कुछ न समझ आये तो पूछ लेना 9455857477

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Chapter 5 Some Natural phenomena
Introduction
The natural phenomenon can be defined as the naturally occurring calamity or
physical process.
Types of the natural phenomenon include
 Thunder
 Weather
 Germination
 Erosion
Some natural phenomena can be destructive such as
 Earthquakes
 Lightning
 Volcanic eruption
 Cyclones
Charged Bodies
What is Charge?
Charge is most commonly used to refer to electric charge. It is a fundamental property
of matter like mass. It is a physical property because of which matter experience a
force in an electromagnetic field.
Electric charges may be positive or negative in nature. If there is no net electric
charge, the matter is considered neutral or uncharged.
Types of charges and their interactions
Charges are of two types
1. Positive charge – When the matter has more protons than the number of
electrons.

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2. Negative charge – When the matter has more electrons than protons. A
negative charged body has excess of electrons.
This concept arose from the fact that when we rubbed a glass rod with silk, the glass
rod gained a positive charge while the silk fabric gained a negative charge.
What are electrons, protons, and neutrons, and where it is present?
Electrons, protons and neutrons are fundamental particles. Electrons are negatively
charged particles that move around the nucleus of an atom.
Protons are positively charged particles. Neutrons are electrically neutral which means
that they carry no charge.
Both protons and neutrons are concentrated at the centre of an atom known as the
nucleus of the atom. Electrons surround the nucleus.
How the object becomes positively charged and negatively charged?
When an object loses electrons, it becomes positively charged because it has more
protons than electrons. After gaining electrons, the objects become negatively
charged.
When a glass rod is rubbed with silk cloth, for example, it becomes positively
charged, whereas the silk cloth becomes negatively charged.
Figure (a) shows a glass rod being rubbed with a silk cloth. Figure (b) shows that on
rubbing with silk cloth glass rod becomes positive in charge because electrons are
rubbed off glass rod. Due to this silk cloth becomes negative.

Charging by rubbing or friction

It means that when two objects rub against each other, electrons are transferred
between them and they become charged.

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For example, rubbing a plastic comb through dry hair charges it. This charged object
(plastic comb) can now attract other charged and uncharged objects. The charged
plastic comb is capable of attracting scraps of paper.
Properties of charge
Like charges repel each other. This means that two positive charges repel each other.
Similarly, two negative charges would also repel each other.
Unlike charges, they attract each other. This means that a Positive-Negative charge
would attract each other.
For example, a charged rubber balloon is repelled by another charged balloon,
whereas an uncharged balloon is attracted by another charged balloon.
like charges repel

unlike charges attract

The reason for repulsion is that both the balloons contain the same type of charge,
whereas attraction happens because both the balloons contain different types of
charge.
Static charge vs Current Electricity
The electric charge produced by rubbing is known as a static charge, whereas charges
that move together form an electric current. A static charge is one that does not move.
Current electricity on the other hand is study of moving charges.
Transfer of Charge
There are two ways to transfer charge from one object to another.

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1. Conduction – When a charged object makes contact with a conductor, charges are
transferred through the conductor. The object gains the same charge as the charged
body. This method requires physical contact between the objects.
2. Induction – When a charged object is brought near a neutral object, the object gets
induced and becomes charged. The object acquires the opposite charge to that of the
charged body. This process doesn't require physical contact.
The transfer of electric charges does not create or destroy charges and in this process
charge remains conserved.
Electroscope
It is a device or an instrument that can be used to test whether an object is carrying a
charge or not. An electrical charge can be transferred from one charged object to
another through a metal conductor. It consists of a metal rod with a thin metal strip or
leaf attached to it at the bottom.
Because gold and silver are good conductors of electricity, they are commonly used to
make electroscopes.
How does the electroscope detect the charge?
 A charged object is brought in contact with the open end of the wire.
 The charges are transferred through the wire, which is a good conductor of
electricity.
 The gold plates also get charged and repel each other as they are similarly
charged.
Discharged bodies
The body is said to be discharged if it loses its charge to the earth or any other body.
Explain why a charged body loses its charge if we touch it with our hand?
When a charged body is touched by our hand, our body conducts its charge to the
earth as the human body is a good conductor of electricity.
The process of transfer of charges from a charged object to the earth takes place is
called earthing.In general, every tall building has earthing to protect it from electrical
shocks caused by electric current leakage.
Lightning – A natural destructive phenomenon
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Lightning is an electric discharge seen in the sky between oppositely charged clouds
or between charged clouds and the earth. Lightning is defined as the transfer of charge
from cloud to another cloud or from one cloud to the earth.
Cause of lightning
Lightning is caused by the accumulation of charges. When negative and positive
charges meet, they produce a streak of bright light accompanied by sound. It causes a
lot of damage.Mostly, lightning occurs within the clouds. Lightning is also caused due
to static electricity.
 During rain, the air current moves upwards and water droplets move
downwards. This movement leads to the separation of charge in a cloud.
 The positive charges accumulate near the upper side and negative charges
collect near the bottom of the cloud, which causes a rearrangement of charges
on the ground surface.
 Thus, positive charges accumulate near the ground surface. When the
accumulated charge becomes high, the flow of charges takes place.
 The flow of charges takes place through the air. However, the air is a poor
conductor of electricity, but the magnitude of accumulated charges becomes
high, causing the air to get ionized.
 When the negative charge meets the ground's positive charge, it results in
streaks of bright light.
 Lightning strikes the highest objects, like tall buildings, bridges, and
monuments, and causes damage. To prevent this damage, lightning protection
systems are installed.

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Lightning Conductor
A metal rod (generally made of copper) placed on top of tall buildings with its lower
end connected to the ground. It is used to protect buildings from the effects of
lightning. When lightning strikes, the metal rod, being a good conductor, provides an
easy passage for the transfer of charge to the ground. This way, the electric discharge
flows from the clouds into the ground without damaging the clouds.
Things to do during lightning
 Switch off the electrical appliances like computer, TV, refrigerator etc.
 If travelling in a car or bus, remains inside the vehicle and shut all its doors
and windows.
 Get inside as quickly as possible.
 Check the forecast before going outside in the monsoon.
Things to avoid during lightning.
 Do not roam here when there is lightning.
 Avoid contact with running water.
 Do not lie on the ground.
 Do not sit in open vehicles.
 Do not carry an umbrella.
Earthquake – Another natural destructive phenomenon
A sudden trembling or shaking of the earth for a short interval of time is caused by
disturbances deep inside the earth's crust. It can cause large-scale destruction. It is not
possible to predict the occurrence of an earthquake. An earthquake produces waves on
the surface of the earth. Earthquakes may be caused by the sliding of tectonic plates.
Sometimes, an earthquake may be followed by aftershocks that occur as the rocks
settle down in their new position.
Why do earthquakes occur?

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 The earth’s crust is made up of fragments called plates, also called tectonic
plates.
 These plates are continuously moving.
 Due to continuous motion, these plates slide past or collide with each other.
 The rocks at the boundaries of these plates get interlocked and prevent the
plates from moving, which results in pressure being formed on these rocks.
 The increase in pressure leads to the slipping of rocks and causes the rocks to
vibrate.
 These vibrations travel up to the surface and cause earthquakes.
Focus, Epicentre and Fault zones
1. Focus:-The point where the earthquake originates or starts is called the focus.
2. Epicentre:-The point on the surface of the Earth immediately above the focus
is known as the epicentre.
3. Fault zones or seismic zones:-Weak zones (The boundaries of the tectonic
plates) where earthquakes are most likely to occur are called fault zones or
seismic zones.
Seismology, Seismic waves, and Seismograph
1. Seismology:- The study of earthquakes is called seismology.
2. Seismic waves:- The waves produced on the surface of the earth in an
earthquake are called seismic waves.
3. Seismograph:- The instrument is used to measure seismic waves.
How can the intensity of an earthquake be measured?
 The destructive energy of an earthquake is measured on the Richter
scale designed by an American Seismologist, Charles F. Richter, using a
seismograph.
 On the Richter scale, an earthquake measuring
o 2 to 4 – It is a mild earthquake and does not cause any damage.

o 4 to 8 – It is moderate to severe.
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o 8 to 9 – It is very severe and destructive earthquakes. It causes a lot of
damage to life and property.
 A major earthquake occurred in India on 8 October 2005 in Uri and Tangdhar
towns in North Kashmir.
 On 26 January 2001, in the Bhuj district of Gujarat, a major earthquake
occurred which caused a lot of damage to life and property.
 Both the Bhuj and Kashmir had a earthquake of magnitude greater than 7.5.
Protection against Earthquakes
People living in seismic zones have to be specially prepared. Firstly, the buildings in
these zones should be so designed that they can withstand major tremors.
 Steps to protect ourselves in an earthquake
 Stay away from tall and heavy objects.
 Take shelter under a table.
 If you are outdoors, stay away from buildings, trees, and overhead power
lines. Try to move to the open ground.
अब इसका SUMMARY HINGLISH मे देता हूँ रटना मत कुछ समझ न आए
तो पूछ लेना|

🔷 Natural Phenomena क्या होते हैं?

Definition: ऐसे physical या biological बदलाव जो naturally
होते हैं, उन्हें natural phenomena कहते हैं।
कुछ harmless होते हैं (weather, germination) जबकि कुछ
destructive भी हो सकते हैं जैसे:
 Lightning
 🌍 Earthquake
 🌋 Volcanic Eruption
 Cyclone

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⚡ Electric Charge and Charging
🔌 What is Charge?
 Charge is a fundamental property just like mass.
 दो प्रकार के charges होते हैं:
1. Positive Charge – अधिक protons
2. Negative Charge – अधिक electrons
🧲 Properties of Charges
 Like charges repel (same-same = repulsion)
 Unlike charges attract (opposite = attraction)
🔁 How objects become charged?
 Friction से – जैसे glass rod को silk से रगड़ने पर charge
transfer होता है।
 Conduction से – Direct contact से charges transfer होते
हैं।
 Induction से – बिना contact के ही nearby होने से charge
induced होता है।
📟 Electroscope
 एक device जिससे check किया जाता है कि कोई body charged
है या नहीं।
 Gold leaves repel if charged.
🧍‍♂️Discharging & Earthing
 जब charged body को जमीन से जोड़ते हैं (जैसे हाथ लगाना),
charge Earth में चला जाता है → Discharge
 Tall buildings में Earthing rod होती है ताकि lightning से
protection मिल सके।

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⚡ Lightning – A Destructive Phenomenon
📈 Cause of Lightning
 Clouds में positive और negative charges बनते हैं।
 Opposite charges attract होते हैं और discharge के समय
तेज़ light + sound produce होता है।
🧲 Lightning Conductor
 Copper rod जो building के ऊपर लगाई जाती है और ground से
जुड़ी होती है।
 Lightning strike होने पर charge safe तरीके से ground
में चला जाता है।
✅ Do's during Lightning
 TV, fridge off करो
 Safe enclosed जगह में रहो
 Forecast check करके बाहर निकलो
❌ Don'ts during Lightning
 Metal umbrella मत पकड़ो
 Tall isolated पेड़ के नीचे मत खड़े हो
 Open ground या vehicles से बचो

🌍 Earthquake – Another Destructive Phenomenon

🌐 Why Earthquakes Occur?
 Earth की crust tectonic plates से बनी होती है।
 Plates टकराती हैं या खिसकती हैं → Stress build होता है →
Vibrations → Earthquake
🔍 Terms to Know
 Focus – जहां earthquake origin होता है
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 Epicentre – Focus के ऊपर Earth की सतह पर point

 Seismic Zones – Fault zones, where earthquakes are

more likely
📈 Richter Scale
 Earthquake की तीव्रता को measure करता है:
o 2-4 → Minor

o 4-6 → Moderate

o 6-8+ → Severe (Bhuj, Kashmir earthquake)

📊 Seismograph
 एक instrument जो seismic waves detect करता है
🛑 Protection during Earthquake
 Table के नीचे छुपो
 Open area में जाओ
 Buildings, poles से दूर रहो
 Schools और homes में earthquake-resistant design का
use हो

⚔️Static vs Current Electricity

Feat Current
Static Electricity
ure Electricity

Moti Charges rest पर रहते Charges flow

on हैं करते हैं

Bulb में
Exam Comb को रगड़ना,
current flow
ple Balloon का stick होना
होना

Natu Temporary और Continuous और

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Feat Current
Static Electricity
ure Electricity

re localized directional

🧠 Quick Revision (Conceptual MCQ style)

1. A body becomes positively charged when—
a) It gains electrons
b) It loses protons
✅ c) It loses electrons
d) It gains protons
2. Electroscope में gold leaves क्यों repel करती हैं?
✅ क्योंकि दोनों में same type का charge होता है।
3. Earthquake की तीव्रता किससे मापी जाती है?
✅ Richter Scale
4. Lightning conductor किस material से बना होता है?
✅ Copper
5. Lightning strikes mostly on—
✅ Tall isolated objects like trees, towers, buildings.

कुछ न समझ आये तो पूछ लेना 9455857477

By Adarsh 54