Electricity
Electricity
It is controllable and convenient form of energy for a variety of uses in home,
schools, hospitals, industries, and so on.
Electric Charge
It is the property associated with the matter due to which it shows some definite
effect like electric field, magnetic field, and electromagnetic field.
Properties:-
Electric charge is a scalar Quantity.
Electric charge is quantised.
Electric charge is invariant.
Net charge can neither be created nor be destroyed it can remain constant.
Electric field
The space around a given charge in which another charge can experience the
force of attraction or repulsion.
Electric Current
When an electric charge is free to move in an electric field, it starts moving in
the direction of force due to field.
The dynamic state of electric charge is called electric current.
I=q/t Ampere = coulomb/second
The S.I unit of current Ampere.
The S.I unit of electric charge coulomb.
1 Ampere: it is constituted by the flow of one coulomb of charge per second.
1 milliamperes = 10-³A
1 micro-ampere = 10-⁶A
Q=ne
Charge on e- = -1.6x10-¹⁹C
1 coulomb contained = 6.25 x10¹⁸ electron
Drift speed = 1mm/s
Drift Speed
A steady current flow through a conductor, the electron in it move with a certain
average, it is drift speed.
Electric circuit
A continuous and closed path of an electric current.
Electric current was considered to be flow of positive charge and the direction
of flow of positive charge was taken to be the direction of electric current.
Ammeter measure electric current and it is connected in series.
Voltmeter measure potential difference and it is connected in parallel.
Electric potential
Electric potential at a point is defined as the work done required in moving a
unit charge from infinity to that point.
(kisi bhi charge ko kisi bhi point pe le jane me jo energy lagti
hai wahi uska potential hai)
Electric potential difference
it is defined as the work done required to move a unit positive charge from one
point to another.
V = W/q volt = joule/coulomb
The S.I unit of electric potential difference is volt (v).
1 volt: it is a potential difference between two points in a current carrying
conductor when 1 joule of work is done to move a charge of 1 coulomb from one
point to the other.
Ohm's Law
If the physical condition of the conductor remain unchanged, the ratio of
potential difference to the flowing current remain constant. i.e. V/I constant
The V-1 graph is a straight line.
V/I is a constant ratio.
V/I = R = constant
Resistance
It is the property of a conductor to resist the flow of charges.
The S. unit of resistance is ohm(Ω).
1 ohm: if the potential difference across the two end of a conductor in TV and
the current through it is 1A, then the resistance 'R' of the conductor is 1 Ω
Current through a resistor is inversely proportional to its resistance.
A component used to regulate current without changing the voltage source
is called variable resistance.
Rheostat is used to change the resistance.
A conductor having some appreciable resistance is called a resistor.
The resistance of a conductor depends on
Resistivity doesn't depend
On its length.
on any of these
On its area of cross-section.
On the nature of its material. {p = rho}
p(rho) is a constant of proportionality and is called the electrical resistivity of
the material of the conductor.
→The S.I unit of resistivity Ω/m.
The metals and alloy have very low resistivity in the range of 10-⁸ m to 10-⁶ m
Insulator have resistivity 10¹² to 10 ¹⁷ m.
Resistance and resistivity of a material vary with temperature.
Alloy do not oxidise (burn) readily at high-temperature that's why they are
commonly used in electrical heating device.
Nichrome -> Nickel, chromium, manganese and iron metal..
P.Y.Q
Question: Elements of electric toasters and electric iron are made of an alloy
rather than a pure metal. Give two reason to justify the statement.
Answer: (a)Alloys do not oxidise readily at high-temperature, so they are more
resistance to corrosion..
(b) Alloys have lower electrical conductivity than pure metals.
Activity 12.1
Calculate the ratio of V to I for each pair of potential difference V and current 1.
Plot a graph between V and I, and observe the nature of the graph.
On increasing the potential difference across a resistance that val see an
increase in the current, it proves that V∝I.
i.e. Ohm's law.
Resistor in series
Value of current in the ammeter is the same.
voltage is not same v =V1+ V₂ + V₃ ........
Requivalent: If the combination of a resistance are replaced by a single
resistance such that same current flows from the same voltage.
In series - device are connected end to end
Disadvantage of series connection
In series connection when one component fail the circuit is broken and a
none of the component works.
It is impracticable to connect an electric devices in series, because they
need currents wildly different value to operate properly.
Resistor in parallel
Advantage of parallel connection
A parallel circuit divides the current through the electrical gadgets.
The total resistance in a parallel circuit is decreased.
P.Y.Q
P.Y.Q
Activity 12.2
Are the ammeter readings different for different components connected in the
gap XY ? What do the above observations indicate?
Observe the ammeter readings in each case. Analyse the observations.
Electric current flows through a component depending upon the resistance of
the component. We use different components in the gap XY such as nichrome
wire, torch bulb, and 10W bulb. conductivity is different for different materials.
since V is constant in the case so according to Ohm's Law
V = IR
so current I become inversely proportional to resistance R
conclusion: Different materials show different conductance or resistance.
P.Y.Q
Question: What is mean by resistance of a conductor? Name and define its si unit. list the factors on
which the resistance of a conductor depends. How is the resistance of a wire affected
(i) if its length is doubled
(ii) its radius is doubled
Answer : It is a position offered to the flow of current by a conductor. Ohm, it is the resistance of a
conductor to which 1 A current flows under a potential difference of one volt.
The factors are-length, area of cross-section, material temperature.
(i) lenath is doubled, resistance is double
(ii) radius is doubled, area of cross-section become four times, so resistance became ane-fourth.
Heating effect of electric current
If the electric circuit is purely resistive, that is, a configuration of resistors only
connected to a battery; the source energy continually gets dissipated entirely in
the form of heat. This is known
P = vq / t = VI H = Vit H=I²RT H = V²t/R
The energy required to maintain continuous flow of free e(that is electric
current) through a conductor is called electrical energy.
The electric iron, kettle, toaster, heater, soldering iron, incandescent bulbs etc.
are work on the application of heating effects of electric current
Joule law of heating
Heat produce in a resistor is.
(i) directly proportional to the square of current for a given resistance.
(ii) directly proportional to the resistance for a given current. (iii) directly
proportional to the time for which the current flow through. H=IRT
Tungsten has high melting point 3380 deg * C is used for making bulb filament.
Electric power
Rate of consumption of electrical energy is known as electrical power.
P = VI = I ²R=V²/R
The S.I unit of electrical power is watt(w).
I Watt: It is the power consumed by a device that carries 1A of current when
operated at a potential difference of 1 watt.
1KW = 1000W
1Wh: One watt hour is the energy consumed when I watt of power is used for
thr.
commercial unit of energy electrical energy is kwh,
1KWH = 1000W * 3600 Sec.
=3.6x10⁶ watt second
=3.6X10⁶ joule (j).
1. calorie 4.3) (approx)
P.Y.Q
P.Y.Q
P.Y.Q
Activity 12.4
Do you find any change in the value of current through the ammeter.
Answer:Reading of ammeter remains constant irrespective of the position.
E.K.Q
1-Electrical resistivity of a given metallic wire depends upon
(a) its length
(b) its shape
(c) its thickness
(d) nature of the material
Ans-(d)
2-What is the maximum & minimum resistance which can be made using five resistors each of
1/5Ω respectively?
3-If the current through a resistor is increased by 100% (assume that temperature
remains unchanged), the increase in power dissipated will be
(al 100%
(b) 300%
(c) 200%
(a) 400%
Ans-b
4-in an electrical circuit three incandescent bulbs A, B, and C of rating 40W,
60W, and 100w, respectively are connected in parallel to an electric source.
Which of the following is likely to happen regarding their brightness?
(al Brightness of all the bulbs will be the same.
(b) Brightness of bulb A will be the maximum.
(C) Brightness of bulb B will be more than that of A.
(d) Brightness of bulb C will be less than that of B..
Ans-C
5-Should the resistance of an ammeter be low or high? Give reason.
Answer: It should be as close to zero as possible. Ideally it should be zero ohm.
If it is non-zero and substantial it will affect the true current.
6-state Ohms law? Does it hold good under all conditions? Comment.
Answer: Ohm's law states that at constant temperature, the current flowing
through a conductor is directly proportional to the potential difference across
its ends.
Ohm's law does not hold under all conditions. Ohm's Law does not hold for non-
ohmic material such as electrolyte.
7-Why is parallel arrangement used in domestic wiring?
Answer: To provide the same potential difference across each electrical
appliance. Because if an appliance gets damaged or is turned off the current
always has other independent dedicated parallel paths to other appliances and
hence every appliance is still works fine.
Question: What is the minimum resistance which can be made using five
resistors each of 1/5Ω
Solution:
#abb jab minimum resistance nikalna ho to resistance ko parralee me jod do.
Question: What is the maximum resistance which can be made using five
resistors each of 1/5Ω
Solution: Resistance of each resistor = 1/5Ω
#abb dekho jab bhi resistance to maximum karna ho to Sare Resistance ko
Series me jod do.
Question: A cylindrical conductor of length I and uniform area of cross section A
has resistance R. Another conductor of length 21 and resistance R of the same
material has area of cross section.
Question: A cell, a resistor, a key and ammeter are arranged as shown in the
circuit diagrams below. The current recorded in the ammeter will be
Answer :- The current recorded in the ammeter will be the same in all the
cases.
#kyunki flowing current component ki arrangements pe depend nhi krti hai
(Jab tak ki vo alag tarike se jude na ho)
series is change into parallel on vice-versa.
