AP Physics 2 : Electric Force Between Point Charges

Example Questions

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Example Question #1 : Electric Force Between Point Charges

Two charges are placed a certain distance apart such that the force that each charge experiences is 20 N. If the distance between the charges is doubled, what is the new force that each charge experiences?

There is no way to determine the new force

Explanation:

To solve this problem, we'll need to utilize the equation for the electric force:

We're told that the force each charge experiences is 20 N at a certain distance, but then that distance is doubled. Thus, the new electric force will be:

Example Question #2 : Electric Force Between Point Charges

What is the force experienced by a  point charge  away from a  point charge?

The point charge experiences no force

Explanation:

The equation to find the force from two point charges is called Coulomb's Law.

In this equation,  is force in Newtons,  is the respective charge value in ,  is radius in meters, and  is the Coulomb constant, which has a value of .

Now, we just plug in the numbers. Note: the charge values are in microcoulombs (the Greek letter , called "mu," stands for micro), which is equal to .

Therefore, the force experienced on either charge is 0.216N of force.

Example Question #3 : Electric Force Between Point Charges

You have two point charges,  and , 3m away from each other. The value of  is , and the force they both experience is . What is the value of ?

Explanation:

The equation for the force between two point charges is as follows:

We have the values for , , , and , so we just need to rearrange the equation to solve for , then plug in the values we have.

Therefore, the value for the second charge is .

Example Question #4 : Electric Force Between Point Charges

Two objects in space are placed  apart. One has a charge of , the second has a charge of . What is the electric force between them?

towards each other

towards each other

away from each other

away from each other

towards each other

towards each other

Explanation:

Use Coloumb's law:

First, convert the charges into coulombs.

Plug in values into Coulomb's law.

Negative electric forces indicate attractive forces. Alternatively, we can reason that since one charge is positive, and the other is negative, the charges will attract.

Example Question #5 : Electric Force Between Point Charges

If charge  has a value of , and charge  has a value of , and the distance between their centers, , is what will be the magnitude of the force on charge ?

None of these

Explanation:

Using coulombs law to solve

Where:

it the first charge, in coulombs.

is the second charge, in coulombs.

is the distance between them, in meters

is the constant of

Converting  into

Plugging values into coulombs law

The magnitude will be the absolute value.

Example Question #6 : Electric Force Between Point Charges

If charge  has a value of , and charge  has a value of , and the distance between their centers, , has a value of , what will be the force on charge ?

None of these

Explanation:

Using coulombs law to solve

Where:

it the first charge, in coulombs.

is the second charge, in coulombs.

is the distance between them, in meters

is the constant of

Converting  into

Plugging values into coulombs law

Magnitude will be the absolute value

Example Question #7 : Electric Force Between Point Charges

Charge has a charge of

Charge  has a charge of

The distance between their centers, is .

What is the magnitude of the force on due to ?

None of these

Explanation:

Using the electric field equation:

Where is

is charge , in

is charge , in

is the distance, in .

Convert  to and plug in values:

Magnitude is equivalent to absolute value:

Example Question #8 : Electric Force Between Point Charges

Charge has a charge of

Charge  has a charge of

The distance between their centers, is .

What is the magnitude of the force on due to ?

None of these

Explanation:

Use Coulomb's law:

Where is

is charge , in

is charge , in

is the distance, in .

Convert  to and plug in values:

Magnitude is equivalent to absolute value:

Example Question #9 : Electric Force Between Point Charges

Charge has a charge of

Charge  has a charge of

The distance between their centers, is .

Determine the magnitude of the electric force on due to .

None of these

Explanation:

Use Coulomb's law:

Where is

is charge , in

is charge , in

is the distance, in .

Convert  to and plug in values:

Magnitude is equivalent to absolute value:

Example Question #10 : Electric Force Between Point Charges

Charge has a charge of

Charge  has a charge of

The distance between their centers, is .

What is the magnitude of the force on due to ?

None of these

Explanation:

Use Coulomb's law:

Where is

is charge , in Coulombs

is charge , in Coulombs

is the distance, in meters.

Convert  to and plug in values:

Magnitude is equivalent to absolute value:

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