Question

In Europe the standard voltage in homes is 240 V insteadof the 120 V used in the United States. Therefore a “200-W” Euro-pean bulb would be intended for use with a 240-V potential difference.(a) If you bring a “200-W” European bulb home to the United States,what should be its U.S. power rating? (b) How much current will the“200-W” European bulb draw in normal use in the United States?

Answer 1

In Europe, the standard voltage in homes is 240 V and in the United States, it is 120 V.

(a) If you bring a “200-W” European bulb home to the United States, what should be its U.S. power rating?

Recall that the power of a bulb is given by

`P=VI`

Where V is the voltage and I is the current.

In Europe, the current flowing through a 200 W bulb is

`I=(P)/(V)=(200)/(240)=0.833\; A`

So, a current of 0.833 A will be flowing through the bulb in Europe.

The equivalent power rating of the bulb in the United States is

`P=VI=120\cdot0.833=100\; W`

So, the equivalent power rating of the bulb should be approximately 100 W.

(b) How much current will the “200-W” European bulb draw in normal use in the United States?​

The rating of the bulb is 200 W and the voltage in the United States is 120 V

So, the current drawn by the bulb is given by

`I=(P)/(V)=(200)/(120)=1.667\; A`

As you can see, the bulb will draw more current if the voltage is reduced to supply the same power.

Therefore, the bulb will draw a current of 1.667 A