*46.  Multiple-Concept Example 9 reviews the concepts that are important to this problem. A light bulb is wired in series with a 144-Ω resistor, and they are connected across a 120.0-V source. The power delivered to the light bulb is 23.4 W. What is the resistance of the light bulb? Note that there are two possible answers.

We know sum of voltages around the circuit is zero, so

 

So voltage across lamp is

 

Current can be found from

 

The last two terms of the above equation provide this equation

 

 

 

So a quadratic formula

Solve for VR

 

 

 

So now we can find the voltage across the lamp

 

or

 

So we find R from

 

or

 

 

 

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This page last updated on June 14, 2018