Physics Chapter Simple Harmonic Motion Conceptual questions

1. Give an example of vibratory motion that is not a simple harmonic motion. Give a
reason of your selection.
Answer: An elastic ball bouncing on a perfectly elastic surface is an example of vibratory motion
that is not elastic. It is because the restoring force for the ball is F=mg which is a constant force
and is independent of ball’s displacement from mean position.
2. At extreme position, velocity is zero but acceleration is maximum in simple
harmonic motion. How can you theoretically explain it?
Answer: In SHM, kinetic energy is maximum at mean position and zero at the extreme positions
while potential energy is zero at mean position and maximum at the extreme positions. Since,
acceleration is rate of change in velocity, maximum change in velocity happens at extreme
position from its initial value of mean, therefore acceleration is maximum.
3. What will happen to acceleration of mass spring system if its mass is doubled?
Answer: According to Newton’s 2nd law, F=ma. This equation tells us that if the mass is doubled,
acceleration will become half of its initial value for constant restoring force.
4. A simple pendulum has time period ‘T’. What will happen to its time period if its
thread length is shorten to half?
Answer: Time period of the simple pendulum is:

If the length of the pendulum is shortened to half of its original length, then new period of
pendulum is

Then
Hence period of new pendulum is decreased by (1/ √2 ) times of original period.

5. A simple pendulum has time period of 4 seconds. Will its time period remain same
or change, if its steel bob is replaced by wood bob of same size.

Answer: Time period of the simple pendulum is:

This equation shows us that time period will remain the same because time period of simple
pendulum is independent of mass of the bob.
6. Same masses are attached to different springs, one is vibrating faster. Why?
Answer: It is because of the difference in spring constants of both springs. Time period of mass
spring system is:
𝑚
𝑇 = 2𝜋√
𝑘
This equation shows us that time period will only by either change in mass or spring constant.
So, if mass is same for both springs, then spring constant should be different.
7. A simple pendulum has time period ‘T’ in Murree. In Karachi, it has different time
period. What would you do to make its time period same as it was in Murree.
Answer: The change in time period of simple pendulum is because of the difference in value of
‘g’ at both locations. In order to make time period same for both locations, length of pendulum
should be shortened enough so that change in value of ‘g’ is compensated.
8. What will happen to the frequency of waves in a ripple tank if time period of electric
vibrator is decreased? What will happen to the wave speed?
Answer: If the time period is decreased, the frequency of waves will be increased because
frequency and time period are reciprocal of each other. The increase in frequency will increase
the wave speed of waves.
9. Why do water waves refract at the boundary of shallow water and deep water in
ripple tank experiment?
Answer: The depth of water affects the speed of waves changing their wavelength. The deeper
the water, the faster the waves travel, and so waves will refract (change direction) when they
enter deeper or shallower water at an angle.
10. Under what conditions are the waves diffracted the most?
Answer: The waves diffract the most when the width of the slit is smaller than the wavelength of
the waves.
 Physics Chapter Sound Conceptual questions
1. Why does sound travel faster in solids than liquids and gases?
Answer: Sound travels faster through solids than through liquids and gases because the
molecules of a solid are closer together and, therefore, can transmit the vibrations
(energy) faster.

2. Why are we able to distinguish between two sounds having same loudness?
Answer: We are able to distinguish between two sounds having same loudness because of
difference in quality of both sounds.

3. Vibrating mobile phone on wooden table sounds louder than held in hand.
Why?
Answer: It is because wooden table has more area than hand and since loudness of sound
is directly proportional to surface area, phone on wooden table sounds louder.

4. During a match in cricket stadium, you see a batsman striking the ball but we
hear stroke sound slightly later. Explain this time difference?
Answer: It is because the speed of light (3×108 m/s) is greater than speed of sound in
air (340 m/s) that spectators watching the cricket game hear the sound of stroke a little
later.
5. How much intensity level increases when intensity of louder sound is double
the intensity of faintest audible sound?
Answer: If the intensity is doubled, the sound intensity level goes up by 10*log(2) = 3.01
decibels (dB).

6. Two singers are singing together simultaneously with intensity level 60dB of
each in a hall.
a. Is intensity of sound in the hall doubled?
Answer: No, the intensity of sound in the hall will not be doubled. It is because intensity
is calculated via logarithmic scale.
b. Is the intensity level of sound is doubled?
Answer: Intensity level of sound can be doubled in this case. However, it will depend
upon constructive interference of waves.

7. If pitch of sound is increased then what is its effect on:

a. Frequency of sound: It will increase.
b. Speed of sound: It will increase because pitch will increase frequency which will
increase speed.
c. Intensity of sound: There will be no effect on intensity.
d. Loudness of sound: There will be no effect on intensity.
e. Wavelength: Wavelength of sound wave can be decreased.

8. Vibrating bodies produce sound. When a pendulum vibrates, we do not hear

its sound. Why?
Answer: Sound is heard only if the body vibrates with a frequency of at least 20
Hz. Frequency of vibration of the pendulum is less than 20 Hz. Hence no sound is
heard when the pendulum vibrates or oscillates in air.

9. Two students are talking in the corridor of your school, you can hear them in
your class room but you cannot see them. Why?
Answer: It is because of the reflecting property of sound waves. When students talk in
corridor, sound waves reflect from walls of corridor and enter in class via door, which
helps us listen them without even seeing them.

10. How do curtains help to reduce loudness of sound?

Answer: Curtains can absorb some part of sound waves and allow small portion to pass
through. Thus, the decrease the amplitude of sound waves which reduces loudness.
11. What steps would you take to stop echoing in a large room?
Answer: Some steps can be:
a. Cover the floor with carpets and rugs.
b. Cover the walls and windows with curtains.
c. Fill the room with soft fabric furniture i.e., sofas.
d. Acoustic panels can also be used.
Physics Class 10th

Chapter 12: GEOMETRICAL

OPTICS

1. Choose the correct option.

Radius of curvature of convex mirror is 20cm, its focal length is:

(a) 40cm (b) 10cm (c) -10cm (d) -20cm

Incident ray of light makes an angle of 30° with plane mirror. What is the angle of reflection of light ray?

(a) 30° (b) 45° (c) 60° (d) 90°

Focal length of concave lens is _______

(a) positive (b) negative (c) infinity (d) zero

A virtual, erect and smaller than object, image is always formed by ________

(a) concave mirror (b) convex lens (c) plane mirror (d) convex mirror

A denser medium has refractive index of 1.5 then critical angle for it is:

(a) 41.8° (b) 39.5° (c) 30.0° (d) 15.5°

Concave lens forms virtual, erect and enlarge image if object is placed ___

(a) between F & 2F (b) before 2F (c) at F (d) between F & C

A concave lens has focal length of 5cm. Find its power?

(a) 20D (b) 0.2D (c) -5D (d) -20D

A magnifying glass has focal length of 5cm then its magnifying power is:

(a) 5 (b) 6 (c) 6.2 (d) 7

Near point of a person lies at 40cm from him. He is suffering from:

(a) far sightedness (b) near sightedness (c) presbyopia (d) no disease

Accommodation in eye is done by:

(a) pupil (b) retina (c) ciliary (d) cornea

EXERCISE CONCEPTUAL QUESTIONS

1. When you look at the front side of polished spoon, your image is inverted and from back of the spoon, your image is erect.
Explain why?

The front side of a spoon is inward curved and behaves like a concave mirror and we know that concave mirror forms real image
which is inverted. And the back of spoon is outward curved and behaves like a convex mirror and we know that convex mirror forms
virtual image which is erect.

2. Which mirror is used by girls for makeup and why?

The spherical mirror used by girls for makeup is concave mirror because when the mirror is placed very near to face such that your
face (object) lies inside its focal length, your image appears virtual, enlarged and erect in the concave mirror which helps you to see
the details of your face and apply a sharp make up on it.

3. Why are large convex mirrors fixed at blind turns of mountains?

Convex mirrors form virtual but smaller image than object. So when it is placed at blind turn of mountain it forms smaller image but
covers both sides of the road, which helps drivers to see two ways and the risks of accident are minimized.

4. Which mirrors are used for rearview of vehicles and why?

Conver mirrors are used for rear view of vehicles because convex mirrors form image smaller than objects and can cover wider area of
the rood which increases the view of driver.

5. If a person is walking in pool, why do his legs appear shorter in water?

It is because of refractional into When light travels from water into air it bends away from the normal. and the virtual image of the legs
appear which is shorter than the original size of the legs.

6. Why do diamonds sparkle brightly?

Diamond sparkle brightly because of three factors;

a. Reflection

Diamond's surface is too smooth and well polished, so inspite of nate transparent medium it reflect part of the light incident on its
surface.

b. Total Internal reflection

As diamond is the most denser medium among all transparent media, so when light enters the diamond it reflects multiple times in the
diamond because of Total Internal reflection.

c. Dispersion:

To some extent, diamonds behave like a prism and disperse the light. As dispersion is not that much So we cannot see seven colors but
we see the diamond sparkling.

7. When white light passes through a prism, it disperses into its seven colours. Why does dispersion take place in prism?
A white light is a combination of seven colours (violet, indigo, blue, green, yellow, orange and red). When the light is incident on a
prism, the seven different colours are refracted at a slightly different angles because of having slight different wavelengths and
dispersion of eight different takes place.

8. Magnifying glass can burn paper. How is it possible?

A magnifying glass is a convex lens which focuses all the light rays incident on it at a single point i.e. its focus. So when light rays
converge at a point, the intensity of light increases and the heat of all rays is focused at a point which is enough to burn a piece of
paper.

9. Your grandfather uses spectacles to read newspaper. You see through the spectacles and you observe that objects behind it
were inverted. Why was it so observed?

The lens used in the glasses is convex which is used to magnify the object, when your grandfather reads the news paper, his eyes lies
in the focal length of the lens so the image of newspaper is virtual, erect and enlarged, But when you see from his glass standing
behind him! You are out of the focal length of the convex lens and the image of newspaper appears real but inverted for you.

10. Under what condition, is a convex lens nearly acts as diverging lens?

When an object is placed inside the focal length of a convex less, the rays don’t actually converge to the opposite side of the lens,
instead they diverge and form virtual image to the same side of the object, which is true for concave (Diverging) lens.

Life is too short for regrets. Give in your all while you still have time.

Good luck happy learning

-Sana Shakeel