Physics Help: Electricity & Circuits

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To find the power dissipated by R3 in a series circuit with a 12V battery and resistors R1=45 ohms, R2=200 ohms, and R3=700 ohms, first calculate the total resistance and then the current using Ohm's law. The voltage across R3 can be determined by finding the voltage drop across the other resistors. Power can be calculated using the formulas P=IV or P=I^2R. Understanding these concepts will help in solving potential difference questions in circuits. Good luck on the test.
MJ
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I have a test tomorrow and I'm having trouble figuring out some of these review problems. Any help would be much appreciated!

1) Find the power dissipated by R3 in a series circuit with a 12V battery with 3 resistors. R1=45ohms R2=200ohms R3=700ohms

I also have a few questions where it asks you to find the potential difference between two points. For example, before and after a resistor in a circuit. How do i do this?

Thank you very much!
 
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Remember that P=IV

You have the total voltage, find the total resistsance. Then find how much voltage is used in R3.
 
Also, P=I^2R. don't forget (or at least learn how to use Ohm's law) all of the power equations. Find total resistance. You should be able to find the circuit current then apply the above eq. Good luck on the test.
 

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