# Electricity

### One Marks Questions

Answer: The flow of charges constitutes an electric current. Electric current is the rate of flow of electric charges.

Answer: A continuous and closed path of an electric current is called an electric circuit.

Answer: Charge of one electron = 1.6 × 10-19 c

a. ampere b. volt

Answer: The electric potential difference between two points in an electric circuit is defined as the work done to move a unit charge from one point to the other.

The total resistance Rs= R1 +R2 + R3

Electric Iron, Electric heater, electric toaster, electric oven, electric kettle and electric heater.

Answer: The bulbs are usually filled with chemically inactive nitrogen and argon gases to prolong the life of the filament.

Answer: Electric power is defined as the rate at which electric energy is dissipated or consumed in an electric circuit.

### Two Marks Questions

Answer: The Joules law of heating states that The heat produced in a resistor is
i. directly proportional to the square of current for a given resistor.
ii. Directly proportional to the resistance for a given current.
iii. Directly proportional to the time for which current flows through the resistor.

Answer: Electric heating is used to produce light in an electric bulb. The filament in the bulb gets hot due to the heating effect of the electric bulb and emits light.

Answer: The bulbs are usually filled with chemically inactive nitrogen and argon gases to prolong the life of the filament.

Ohm’s law states that “The potential difference, V, across the ends of a given metallic wire in an electric circuit is directly proportional to the current flowing through it, provided its temperature remains the same.”

charge = 20 coulomb
We know that potential difference =

work done / charge

Potential difference =
100 / 20

= 5 volt

The rheostat is the variable resistor. It means its resistance can be varied. The rheostat is used to change the value of current in a circuit without changing the voltage source.

The motion of electrons in an electric circuit constitutes an electric current. The electrons, however, are not completely free to move within a conductor. They are restrained by the attraction of the atoms among which they move. Thus, the motion of electrons through a conductor is retarded by its resistance.

(a) We are given,
V = 220 V
R = 1200 Ω
we have I =

V / R

current I =
220 V / 1200 Ω

current I = = 0.18 A

(b) We are given,
V = 220 V
R = 100 Ω
current I =
220 V / 100 Ω

current I = = 2.2 A.

### Three and Four Marks Questions

i. Length of a conductor :
The resistance of a uniform metallic conductor is directly proportional to the length (l) of a conductor.

ii. Area of cross-section :
The resistance of a conductor is directly proportional to its area of cross-section(A)

iii. Nature of material :
The resistance of the conductor depends on the nature of the material in which it is made.

iv. Temperature :
Resistance of the conductor increases with an increase in temperature.

When heating at max rate,
power, P = 840W
V = 220V
We know P = VI
⇒ 840 = 220 × I
⇒ I =

840 / 220

⇒ I = 4 A

R = V/I =
220 / 4
= 55 Ω
So current = 4 A and resistance = 55 Ω

When heating at minimum rate,
power, P = 360 W
V = 220 V
We know P = VI
⇒ 360 = 220 × I
⇒ I =
360 / 220

⇒ I = 1.636 A
R =
V / I
=
220 / 1.636
= 134.45 Ω
So current = 1.636 A and
resistance = 134.45 Ω

Potential difference = V = 5 V
Current = I = 500 mA = 0.5 A

i. Power = V X I
= 5x0.5
= 2.5 W

ii. Reistance = R = ?
By Ohm's law: V = IR
R =

V / I

R =
5 / 0.5

=
50 / 5

= 10 Ω

iii. Energy consumed when it is lighted for 4 hours
Energy = Power x time
Energy = 2.5x4x60x60
Energy = 36000 joules/sec