Question

Calculate the current through a 60 W lamp rated for 250 V. If the line voltage falls to 200 V, how is the power consumed by the bulb affected?

Answer 1

Given,

Power (P) = 60 W

Voltage (V) = 250 V

We know that,

Power (P) = VI

Substituting the values in the formula above, we get,

`60 = 250 xx "I"`

`=> "I" = 60/250`

`=> "I" = 0.24 A`

Hence, current through the lamp = 0.24 A

Power consumed when voltage is 200 V = ?

Resistance of lamp (R) = `"V"^2/"P"`

Substituting the values in the formula, we get,

R = `250^2/60`

⇒ R = 1041.6 Ω

From relation,

P = `"V"^2/"R"`

Substituting the values in the formula, we get,

P = `200^2/1041.6`

⇒ P = 38.4 W

Hence, power consumed reduces to 38.4 W.