# What resistance is needed if current is .300 A?

1. May 15, 2008

### pebbles

1. The problem statement, all variables and given/known data
A 75.0 W bulb is connected to a 120 V source. A lamp dimmer puts a resistance in series with the bulb. What resistance would be needed to reduce the current to .300 A?

2. Relevant equations
R=V/I

3. The attempt at a solution

R=120/.3A=400 ohms. The answer is 210 ohms. What am I missing?

2. May 15, 2008

### Phrak

Here's another relevant equation.

$$(R_{bulb} + R_{dimmer} = V_{total}/I$$

3. May 15, 2008

### montoyas7940

Here is one more:

$$P=V^2/R$$