AP Physics 2 : Ohm's Law

Example Questions

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Example Question #1 : Ohm's Law

What is the current through the battery in the above circuit?

Explanation:

First, find the total resistance of the circuit. Since the resistors are in parallel, use the following formula:

Plug in known values.

Next, use Ohm's law to find current.

Plug in known values.

Example Question #2 : Ohm's Law

There are 3 resistors in series. Their resistances are, in order, , and . The total potential drop is . What is the potential drop across the second resistor?

Explanation:

Use Ohm's law to find the current passing through each resistor. Because they are in series, they have the same amount of current. Once we get the current, we can plug in the resistance for each resistor to find its potential drop.

Now, find the potential drop across the  resistor.

Therefore, the potential drop across the  resistor is

Example Question #1 : Ohm's Law

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

There's not enough information to find the resistance

Explanation:

Even though there is no resistor, Ohm's law still applies. Use it to find the resistance of the wire.

The resistance of the copper wire is

Example Question #2 : Ohm's Law

In the circuit above, find the voltage drop across .

None of these

Explanation:

First, find the total resistance of the circuit.

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

Next, add the series resistors together.

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

Since  and  are in parallel, they will have the same voltage drop accross them.

Example Question #5 : Ohm's Law

In the circuit above, find the current through .

None of these

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 #6 : Ohm's Law

In the circuit above, find the current through .

None of these

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.

In series, all resistors will have the same current.

Thus, the current through  is the same as through the rest of the circuit.

Example Question #7 : Ohm's Law

In the circuit above, find the voltage drop across .

None of these

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.

and  will have the same voltage drop across them, as they are in parallel, and are equivalent to the combined resistor

Example Question #3 : Ohm's Law

In the circuit above, find the voltage drop across .

None of these

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.

and  will have the same voltage drop across them, as they are in parallel, and are equivalent to the combined resistor

Example Question #9 : Ohm's Law

What is the total resistance of the circuit?

None of these

Explanation:

, , and are in parallel, so we add them by using:

We find that

, , and  are in series. So we use:

Example Question #10 : Ohm's Law

What is the current flowing through ?

None of these

Explanation:

, , and are in parallel, so we add them by using:

We find that

, , and  are in series. So we use:

First, we need to find the total current of the circuit, we simply use:

Because and  are in parallel,

Also, the voltage drop must be the same across all three

Using

Using algebraic subsitution we get:

Solving for

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