## Series Wiring

1. The problem statement, all variables and given/known data

A 60W lamp is placed in series with a resistor and a 120V source. If the voltage across the lamp is 25V, what is the resitance R of the resistor?

2. Relevant equations

I derived R= V2/P from ohm's law to solve this problem.

3. The attempt at a solution

R= V2/P
=(25V)2/60W
=10.4 ohms

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 Recognitions: Homework Help Science Advisor That's the resistance of the lamp. Remember the current in the lamp an the resistor is the same, whats the voltage rop accross the resistor?
 120v - 25v = 95v?

## Series Wiring

I guess I just don't understand what voltage to use and why.
 Recognitions: Homework Help Science Advisor You have 120V total, 25V accross the lamp and so (120-25) across the resistor To work out the resistance you need the current through the resistor This is the same as the current through the lamp hint: Power = current * voltage difference
 I=P/V =60W/(120V-25V) =0.63 A R=V/I =95V/0.63A =151 ohms?
 Recognitions: Homework Help Science Advisor sounds good
 Thank you so much for your help!