AP Physics 2 : Circuits

Study concepts, example questions & explanations for AP Physics 2

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Example Questions

Example Question #21 : Circuit Properties

A single  resistor is added in series to a circuit with a  battery. Determine the current.

Possible Answers:

Correct answer:

Explanation:

Use Ohm's law:

Converting  to 

Example Question #21 : Circuits

Combined circuit

In the circuit above, find the current through .

Possible Answers:

None of these

Correct answer:

Explanation:

First, find the total resistance of the circuit.

 and  are in parallel, so we find their equivalent resistance by using the following formula:

Next, add the series resistors together.

Use Ohm's law to find the current in the system.

The current through  and  needs to add up to the total current, since they are in parallel.

 

Also, the voltage drop across them need to be equal, since they are in parallel.

Set up a system of equations.

Solve.

Example Question #21 : Circuits

In the circuit diagram shown below, both resistors have a resistance of  ohms. If resistor  were to be removed from the circuit altogether, how would the current through  change?

Voltage

Possible Answers:

The current will halve

The current will not change

The current will double

The current will decrease by a factor of 

The current will increase by a factor of 

Correct answer:

The current will not change

Explanation:

In this question, we're shown a circuit diagram with two resistors connected in parallel. We're also told that both resistors have the same resistance. We're then asked to determine how the current through one of the resistors will change if the other one is removed.

To answer this question, we'll need to take Ohm's law into account, which states the following.

Moreover, for two resistors connected in parallel, the equivalent resistance is found by summing the inverses of the individual resistors. In the event that two resistors have the same value, as in this case, the equivalent resistance will be cut in half.

Since the equivalent resistance of the circuit is half as great as either resistor, the removal of  will cause the overall resistance of the circuit to become twice as great. When the resistance becomes twice as great, and voltage does not change, the current through the circuit will become halved.

Now, it's important to realize that the current of the entire circuit becomes half as great. But remember that in the original circuit, the overall current (which was twice as great) was split between the two resistors. Thus, even though the overall current in the circuit is being cut in half, the entirety of the new current is flowing solely through . Therefore, the current flowing through this circuit does not change, even though the current for the entire circuit does.

Example Question #22 : Circuits

You have a circuit with a  resistor connected to a  battery. What is the current through the resistor?

Possible Answers:

Correct answer:

Explanation:

To find the current in a circuit with a battery and resistor(s), you use Ohm's Law.

We have the voltage and we have the resistance, so we don't need to rearrange the equation.

Therefore, the current through the resistor is 2 amps ().

Example Question #21 : Circuits

A  battery produces a  current in a piece of wire. What is the resistance of the wire?

Possible Answers:

There's not enough information to determine the resistance of the wire

Correct answer:

Explanation:

The relevant equation for this problem is Ohm's law.

We're given the voltage and the current, so we need to rearrange to get the resistance.

Example Question #1 : Current And Voltage

Consider a circuit connected to a  battery that has a resistance of . How many moles of charge pass through this circuit within a 30s period?

Possible Answers:

Correct answer:

Explanation:

To begin with, we'll need to calculate the current that is flowing through this circuit. We can do this by using Ohm's law.

Now that we have an expression that gives us the current, which is in units of charge per second, we'll need to calculate the moles of charge per second.

This expression directly above gives the total amount of charge that passes within a given time frame. But to find the moles of charge, we'll need to use Faraday's constant.

Example Question #2 : Current And Voltage

3 sets of parallel resistors

 

Determine the current through .

Possible Answers:

Correct answer:

Explanation:

First, we need to find the total resistance of the circuit. In order to find the total resistance of the circuit, we need to combine all of the parallel resistors first, then add them together as resistors in series.

Combine  with :

Combine  with :

Combine  with :

Then, add the combined resistors, which are now all in series: 

 

Then, we will need to use Ohms law to determine the total current of the circuit

Combine all of our voltage sources: 

Plug in our values:

We know that the voltage drop across parallel resistors must be the same, so:

Use Ohm's law:

We also know that:

Substitute:

Solve for :

Example Question #2 : Current And Voltage

3 sets of parallel resistors

 

Determine the current through .

Possible Answers:

Correct answer:

Explanation:

First, we need to find the total resistance of the circuit. In order to find the total resistance of the circuit, we need to combine all of the parallel resistors first, then add them together as resistors in series.

Combine  with :

Combine  with :

Combine  with :

Then, add the combined resistors, which are now all in series: 

Then, we will need to use Ohm's law to determine the total current of the circuit: 

Combine all of our voltage sources: 

Plug in our values:

We know that the voltage drop across parallel resistors must be the same, so:

Use Ohm's law:

We also know that:

Substitute: 

Solving for :

We plug in our values:

Example Question #5 : Current And Voltage

3 sets of parallel resistors

 

Determine the current through .

Possible Answers:

Correct answer:

Explanation:

First, we need to find the total resistance of the circuit. In order to find the total resistance of the circuit, we need to combine all of the parallel resistors first, then add them together as resistors in series.

Combine  with :

Combine  with :

Combine  with :

Then, add the combined resistors, which are now all in series: 

Then, we will need to use Ohms law to determine the total current of the circuit.

 

Combine all of our voltage sources: 

Plug in our values:

We know that the voltage drop across parallel resistors must be the same, so:

Use Ohm's law:

We also know that:

Substitute: 

Solve for :

Plug in our values:

Example Question #1 : Current And Voltage

3 sets of parallel resistors

 

Determine the current through .

Possible Answers:

Correct answer:

Explanation:

First, we need to find the total resistance of the circuit. In order to find the total resistance of the circuit, we need to combine all of the parallel resistors first, then add them together as resistors in series.

Combine  with :

Combine  with :

Combine  with :

Then, add the combined resistors, which are now all in series: 

Then, we will need to use Ohm's law to determine the total current of the circuit.

Combine all of our voltage sources:

Plugin our values:

We know that the voltage drop across parallel resistors must be the same, so:

Use Ohm's law:

We also know that:

Substitute: 

Solving for :

Plug in our values:

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