# Resistance of a light bulb question

Hey guys I am having some trouble with this simple questions:
What is the resistance of a light bulb that uses an average power of 75.0 W when connected to a 60.0 Hz power source having a maximum voltage of 190 V?

(b) What is the resistance of a 120 W bulb?

I tried doing it by (75/190)^2 * (2pi60) but this is not correct.

Astronuc
Staff Emeritus
One has to apply the equivalent of P = V I = V2/R = I2R for AC, so R = V2/P.

Since it is pure resistance, i.e. no reactance, the voltage and current are in phase.

Think of average and maximum.

Ok, do i still have to multiply the 60hz by 2pi? Also, how do i handle it being connected to the power source?

no but thanks for the link. I think that should of helped me get an idea