Question

An electric bulb is rated 250 W, 230 V. What information does this convey? 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

'An electric bulb is rated 250 W-230V'; means that if the bulb is lighted on a 230V supply it consumes 25 ow electrical power or 25 OJ of electrical energy converts into heat and light in 1 second.

The safe Ii m it of current through the bulb is:

I = `"P"/"V" = 250/230` = 1.1 A

Current through a 60W lamp rated for 250V is:

I = `"P"/"V" = 60/250` = 0.24 A

We know that resistance of an appliance remains constant.
Resistance of the 1 amp =

R = `"P"/"I"^2 = 60/(0.24)^2 Omega`

If the line voltage falls to 200 V, power =

P = `"V"^2/"R" = (200 xx 200 xx (0.24)^2)/60` = 38.4 watt

Thus power of the lamp reduces to 38. 4 watt.