AP Physics 1 : Electricity

Study concepts, example questions & explanations for AP Physics 1

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Example Questions

Example Question #212 : Electricity And Waves

Which of the following wires with a current running through them would have the least resistance?

Possible Answers:

They would all have equal resistance

Wire B:  and 

Wire C:  and 

Wire D:  and 

Wire A:  and 

Correct answer:

Wire B:  and 

Explanation:

The correct answer is Wire B with  and  of current.

The formula for voltage, current and resistance is as follows:

Thus, the wire with the lowest ratio of voltage to current will have the least resistance.

Example Question #11 : Current And Voltage

Series curcuit

What is the current in the given circuit if  and ?

Possible Answers:

Correct answer:

Explanation:

To find the current we must first find the equivalent resistance. For resistors in series, the equivalent resistance is 

For this problem

Now we use Ohm's law, , to find the current, 

Example Question #1363 : Ap Physics 1

Parallel circuit

What is the current in the given circuit if  and ?

Possible Answers:

Correct answer:

Explanation:

To find the current we must first find the equivalent resistance. For resistors in parallel, the equivalent resistance is 

For this problem

Now we use Ohm's law, , to find the current, 

Example Question #21 : Current And Voltage

What is the current in the given circuit if  and ?

Possible Answers:

Correct answer:

Explanation:

To find the current we must first find the equivalent resistance. This problem is a combination of resistors in series and parallel. First we find the equivalent resistance of resistors in series.

For resistors in series, the equivalent resistance is:

For this problem

The resistors in series can be treated as one  resistor. Now we address the resistors in parallel. For resistors in parallel, the equivalent resistance is:

For this problem

Now we use Ohm's law, , to find the current, 

Example Question #1 : Resistivity

Consider the circuit:

Circuit_4

The current flowing through the entire circuit is . What is the value of R3?

Possible Answers:

Correct answer:

Explanation:

We know the voltage and total current of the circuit, so we can calculate an equivalent resistance using Ohm's law:

Now we can use the expression for condensing parallel resistors to calculate R3:

Example Question #1 : Resistivity

Which of the following factors would decrease the resistance through an electrical cord?

Possible Answers:

Increasing the resistivity

Increasing the length of the cord

Decreasing the cross-sectional area of the cord

Increasing the cross-sectional area of the cord

Correct answer:

Increasing the cross-sectional area of the cord

Explanation:

The equation for resistance is given by .

From this equation, we can see the best way to decrease resistance is by increasing the cross-sectional area, , of the cord. Increasing the length, , of the cord or the resistivity, , will increase the resistance.  

Example Question #3 : Resistivity

An electrician wishes to cut a copper wire  that has no more than  of resistance. The wire has a radius of 0.725mm. Approximately what length of wire has a resistance equal to the maximum  ?

Possible Answers:

2.6cm

960m

38m

9.6m

10cm

Correct answer:

960m

Explanation:

To relate resistance R, resistivity , area A, and length L we use the equation.

Rearranging to isolate the quantity we wish to solve for, L, gives the equation . We must first solve for A using the radius, 0.725mm.

Plugging in our numbers gives the answer, 960m.

Example Question #141 : Electricity

What is the current in a circuit with a  resistor followed by a  resistor that are both in parallel with a  resistor? The voltage supplied to the circuit is 5V.

Possible Answers:

Correct answer:

Explanation:

Resistors in serries add according to the formula:

Resistors in parallel add according to the formula:

We can find the total equivalent resistance:

Now we can use Ohm's law to find the current:

Solve: 

 

Example Question #2 : Resistivity

Basic circuit

In the circuit above, your aim is to limit the current to , so you must design a resistor to serve in the place of .

To make this resistor, you have a spool of mystery metal, which has a cross sectional area of  and a resistivity of, . What length of wire should you cut?

Possible Answers:

Correct answer:

Explanation:

First, find out how much total resistance should be in the circuit in order to get the desired current:

Determine what the second resistance should be.

Find the necessary length of wire.

Example Question #1 : Resistivity

What is the resistance of a  length of round copper wire with a radius of ?

 

Possible Answers:

Correct answer:

Explanation:

Resistance and resistivity are related as follows:

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