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# AP Physics 1 Review of Charge and Circuits

In this video David quickly explains each charge and circuit concept and does a sample question for each one. Created by David SantoPietro.

## Want to join the conversation?

• why do you divide by area to find the resistance of a cylindrical resistor? wouldn't a wider resistor have higher resistance?
• No, the larger the area the leass the resistance. Unlike the lenght . As is increase resistance increases.
(1 vote)
• at isn't the voltmeter measuring the resistance between the parallel resistor and not the one 8 ohm one.
(1 vote)
• Voltmeter or ohmmeter? Voltmeters don't measure resistance, they measure potential difference.
• At we see three equations to solve for power. in equation one P=I^2R this indicates power is directly proportional to current and resistance. However, in the third one we see that P=V^2/R this indicates power is directly proportional to voltage and inversely proportional to resistance, but how is that possible. Did I miss something?
(1 vote)
• V = IR so both of those are true.

P = I^2R indicates power proportional to R, if I is held constant. But if you just increase R and do nothing else, I will go down.
P = V^2/R indicates power inversely proportional to resistance if V is held constant.
• in the example circuit problem, the equivalent resistance of the first two in parallel is 4 ohms. The voltage going into them is 24 volts, so the current going through that equivalent resistance has to be 6. And since the parallel equivalent is in series with the 8ohm, wouldn't that make the 8 ohm also 6 amps, im confused
(1 vote)
• What would happen in a circuit with no resistors?

Also, addressing the circuit that had 6 ohm and 12 ohm resistor in parallel and the 8 ohm resistor in series, does the current through the circuit decrease if you pop enough resistor in series between the current resistors?
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• At how would you solve for the current going through the 6 ohm resistor and the 12 ohm resistor?
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• One way to do this is by using the loop equation to find the voltage going through the parallel. Keep in mind, the voltage for the resistors is the voltage that comes out. Because the voltage is the same for both the resistors in the parallel, simply plug the found voltage into the equation and find the currents.
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• How is the 8 in series with 6 and 12 and not a parellel?
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• The 6 and 12 are in parallel, right? We are considering both resistors to be a single equivalent resistor of 4 ohms. If you were to remove the 2 resistors and replace them with a single equivalent resistor in the diagram it would be on series with the 8 ohm resistor.
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• is there a difference on distribution of two different charges if it is charged with induction or contact?
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• Is it necessary to know the charge of a proton and electron for the ap test? Or will that be given?
• Given, but you should be familiar with the relative sizes.
(1 vote)