Question

what is the difference between power rated and power consumed by a bulb?

Answer 1

Suppose, An electric bulb is rated as 230 V AC, 100 W ( This is called rating of bulb i.e 100 W,). if this bulb is given supply of 230 V AC it will dissipate 100 W energy in one hour.

Now as per ohm’s law - V=I * R

and power P = V * I

so, p = V* I = V * V/R = V.V/R = I * I * R = I.I.R

so Resistance of the bulb R = V.V/P = 230 *230/100=529 ohms

so rated current I = V/R = 230/529 = 0.434 Amps

Now suppose if voltage available is 200 V

then P = V*V/R= 200 * 200/529 =75.6 W ( this is power dissipation at input voltage of 200 V)