Question

The p.d across the lamp is 12v. How many joules of electrical energy are changed into light and heat when

a) a charge of 1C passes through it,
b) a charge of 5C passes through it,
c) a current of 2A flows in it for 10s?

Answer 1

Potential difference across lamp = 12 V

a) When charge q = 1 C passes

Electrical Energy = qV

Electrical Energy = 12 × 1

Electrical Energy 12 Joules

b) When charge q = 5 C passes

Electrical Energy = q × V

Electrical Energy = 5 × 12

Electrical Energy = 60 Joules

c) When current (I) = 2 A flows

Time (t) = 10 seconds

Electrical Energy = V × I × t

Electrical Energy = 12 × 2 × 10

Electrical Energy = 240 Joules