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Homework Help: What resistance is needed if current is .300 A?

  1. May 15, 2008 #1
    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

    3. The attempt at a solution

    R=120/.3A=400 ohms. The answer is 210 ohms. What am I missing?
  2. jcsd
  3. May 15, 2008 #2
    Here's another relevant equation.

    [tex](R_{bulb} + R_{dimmer} = V_{total}/I[/tex]
  4. May 15, 2008 #3
    Here is one more:

    [tex] P=V^2/R [/tex]
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