AP Physics C: Mechanics : Using Ohm's Law

Study concepts, example questions & explanations for AP Physics C: Mechanics

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Example Questions

Example Question #2 : Circuit Relationships

A cicuit with a voltage source of 40V has a  resistor and a  resistor in series, followed by two  resistors in parallel. After the parallel branches rejoin, there is a  resistor before the circuit is closed at the voltage source.

What is the current supplied by the source?

Possible Answers:

Correct answer:


The current supplied by the source can be calculated using a derivation of Ohm's law:

Start by finding the equivalent resistance of the circuit.

Sum the first two resistors in series:

Calculate the equivalent resistance of the two resistors in parallel:

Now, all of the reistances can be viewed as being in series.

Returning to our current calulation, we can find our final answer:

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