Question

Calculate the energy transferred when 2 A current flows through a 10 Ω resistor for 30 minutes. b) Calculate the amount of charge that would flow in one hour through the element of an electric iron drawing a current of 0.4 amps.

Answer 1

a.) 7200 J

b.) 1440 C $\:$

☯ Concept ☯

> When an electric current is passed through a conductor, it generates heat due to the hindrance caused by the conductor to the flowing current. The work done in overcoming the hindrance to the current generates heat in that conductor.

> Power = Work Done / Time Taken

or,

⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀P = W / t

Since,

>Potential Difference = Work Done / Charge

or,

⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀V = W / Q

P = VQ / t

or

P = VI,

where

>I (current) = Charge / Time Taken

Energy supplied by power source to a circuit in time t is,

⠀⠀⠀⠀⠀⠀⠀⠀⠀H = P x t = VIt

Or from Ohm’s law,

⠀⠀⠀⠀⠀⠀⠀⠀⠀H = I²Rt

This is known as Joule’s law of heating. It states that heat produces in a circuit is directly proportional to the square of current flowing, resistance for current and time for which current flows

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(a) Calculate the energy transferred when 2 A current flows through a 10 Ω resistor for 30 minutes

Given :-

Current (I) = 2A

Resistance (R) = 2ohm

Time (t) = 30mins = 1800 sec

Energy = ?

H = I^2 RT

H = 2^2 x 10 x 1800

H = 4 x 18000

H = 72000 J

•°• 7200 Joules of energy is transferred.

(b) Calculate the amount of charge that would flow in one hour through the element of an electric iron drawing a current of 0.4 amps.

Given :-

Time (t) = 1 hr = 3600 sec

Current (I) = 0.4 A

Charge (Q) = ?

We know that,

I = Q/T

Or,

Q = IT

Substituting values,

Q = 3600 x 0.4

Q = 1440 C

•°• A charge of 1440 C flows through the element of the electric iron.

☯ Important Questions ☯

> : If an electric heater consumes electricity at the rate of 500W and the potential difference between the two terminals of electric circuit is 250V, calculate the electric current and resistance through the circuit.

> : An electric geyser consumes electricity at the rate of 1000W. If the potential difference through the electric circuit is 250 V, find the resistance offered by geyser and electric current through the circuit.

> : An electric heater having resistance equal to 5Ω is connected to electric source. If it produces 180 J of heat in one second, find the potential difference across the electric heater.

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