What resistance is needed if current is .300 A?

AI Thread Summary
To reduce the current to 0.300 A for a 75.0 W bulb connected to a 120 V source, a total resistance of 400 ohms is calculated using the formula R=V/I. However, the correct resistance needed is 210 ohms, indicating a misunderstanding in the calculations. The total resistance in the circuit should account for both the bulb's resistance and the dimmer's resistance. The relevant equations include R_total = V_total/I and P = V^2/R. Clarification on the bulb's resistance is necessary to resolve the discrepancy.
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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?
 
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Here's another relevant equation.

(R_{bulb} + R_{dimmer} = V_{total}/I
 
Here is one more:

P=V^2/R
 

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