What resistance is needed if current is .300 A?

  • Thread starter pebbles
  • Start date
  • #1
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Homework Statement


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?


Homework Equations


R=V/I


The Attempt at a Solution



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

Answers and Replies

  • #2
4,254
1
Here's another relevant equation.

[tex](R_{bulb} + R_{dimmer} = V_{total}/I[/tex]
 
  • #3
361
21
Here is one more:

[tex] P=V^2/R [/tex]
 

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