Question

A halogen light bulb is designed to produce 750 Watts at 240 Volts AC. At room temperature, the filament resistance is about 4.8 Ohms. The resistance during operation is about

Answer 1

We know that,

P(power) =Voltage (volts) * current (amps)

by Ohm’s law I(current) =V(volts)/R(resistance)

So P=V*(V/R)

Solving for R

R=V^2/P

Here, P= 750 Watts;V=240 V;

so, R=(240)^2/750=76.8 ohms.

But filament is also offering resistance r=4.8 ohms.

So effective Resistance Req=R+r=76.8+4.8=81.6 ohms (Resistance in series add up)