# AP Physics 1 : Ohm's Law

## Example Questions

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### Example Question #1 : Ohm's Law

Consider the circuit:

If each resistor has a value of , how much current is flowing through the circuit?

Explanation:

First we need to calculate the equivalent resistance of the circuit using the following expression for condensing parallel resistors:

Now we can use Ohm's law to calculate the current flowing through the circuit:

### Example Question #1 : Ohm's Law

A light bulb requires 60 W to function properly. If it is connected to a powersupply of 120 A and functions properly, then what is the resitance of the light bulb?

Explanation:

First, identify the given information:

Two equations are required for this problem:

1.) Ohm's law,

2.) Electrical power

Using the equation for electrical power, we can rearrange to solve for :

At this point, we can substitute in the known values and determine the voltage:

Ohm's law can then be rearranged to solve for the resistence of the light bulb:

The known voltage value then can be substituted into Ohm's law to determine the resistance of the light bulb:

### Example Question #3 : Ohm's Law

What is the resistance of a resistor if the current going through it is  and the voltage across it it is ?

Explanation:

Use Ohm's law.

Plug in known values and solve for resistance.

### Example Question #2 : Ohm's Law

What is the voltage across a resistor with a resistance of  that has a current of  going through it?

Explanation:

Use Ohm's Law.

### Example Question #3 : Ohm's Law

What is the current through a resistor if the resistor has a resistance of  and the voltage across the resistor is ?

Explanation:

Use Ohm's law.

### Example Question #4 : Ohm's Law

If the current through a  resistor is , what is the voltage across the resistor?

Explanation:

UseOhm's law.

Plug in known values and solve.

### Example Question #7 : Ohm's Law

The voltage measured from a point between  and  to the ground is

What is the resistance of  ?

Explanation:

Begin by finding the total resistance in the circuit.

Now note that the voltage identified in the problem is the same as the voltage drop across the second resistor:

Now, since  and  combine to form the total resistance:

### Example Question #5 : Ohm's Law

, and the voltage measured from a point between  and  to the ground is

In the circuit above, what is the resistance of ?

Explanation:

Begin by finding the total resistance in the circuit.

Now note that the voltage identified in the problem is the same as the voltage drop across the second resistor:

### Example Question #115 : Electricity And Waves

is composted of two resistors in parallel,  and

is a single  resistor.

In the circuit above, what is the current?

Explanation:

To find the current, first find the total resistance of the circuit. Begin by simplifying , the two resistors in parallel as follows:

Since  and  are in series, their combined resistance is:

Use Ohm's law to find the current.

### Example Question #6 : Ohm's Law

A resistor with a resistance of  has a current flowing through it of 5A. What is the potential drop across the resistor?

Explanation:

Ohm's law states that the potential drop across a resistor is equal to the product of the current flowing through the resistor and the resistance of the resistor:

We were given the current, I, and the resistance, R, so we simply multiply the two together to get our final answer.

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