# The PD across a lamp is 12V. How many joules of electric energy is changed into heat and light when: a) a charge of 1C passes through it?b) a charge of 5C passes through it?c) a current of 2A flows through it for 10s?

Given: The potential difference across a lamp = 12v

a) To find: We have to find how many joules of electric energy is changed into heat and light when 1C passes through the lamp.

Solution: We know that,

$v=\ \frac{W}{ \begin{array}{l} Q\ \end{array}}$

=> Work done(W) = PD x Charge = 12 x 1 = 12J

b) To find: We have to find how many joules of electric energy is changed into heat and light when 5C passes through the lamp.

Solution: We know that,

$v=\ \frac{W}{ \begin{array}{l} Q\ \end{array}}$

=> Work done(W) = PD x Charge = 12 x 5 = 60J

c)  To find: We have to find how many joules of electric energy is changed into heat and light when a current of 2A flows for 10 seconds through the lamp.

Solution: We know that,

Q = I x t

=> Q = 2 x 10 =  20C

Now,

$v=\ \frac{W}{ \begin{array}{l} Q\ \end{array}}$

=> Work done(W) = PD x Charge = 12 x 20 = 240J

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