N Europe the standard voltage in homes is 220 V instead of the 120 V used in the United States. Therefore "100-W" European bulb would be intended for use with a 220-V potential difference.

(a) If you bring a "100-W" European bulb home to the untied States, what should be its US power rating?

(b) How much current will the 100-W European bulb draw in normal use in the United States?

Given Information:

Peurope = 100 watts

Veurope = 220 volts

Vusa = 120 volts

Required Information:

Pusa = ?

Iusa = ?

Answer:

Pusa = 29.75 watts

Iusa = 0.247 A

Explanation:

The power dissipated in a bulb is given by

P = V²/R

Where P is the power in Watts, V is the potential difference or voltage in Volts and R is the resistance in Ohms

First we have to determine the resistance of the bulb which doesn't change whether the bulb is in the Europe or USA

R = V²/P

R = 220²/100

R = 484 ohms

(a) If you bring a "100-W" European bulb home to the untied States, what should be its US power rating?

Pusa = V²/R

Pusa = 120²/484

Pusa = 29.75 watts

(b) How much current will the 100-W European bulb draw in normal use in the United States?

V = I*R

Vusa = Iusa*R

Iusa = Vusa/R

Iusa = 120/484

Iusa = 0.247 A

Another method:

P = V*I

Pusa = Vusa*Iusa

Iusa = Pusa/Vusa

Iusa = 29.75/120

Iusa = 0.247 A

Hence we got the same current as before.