### All AP Physics C Electricity Resources

## Example Questions

### Example Question #31 : Electricity And Magnetism Exam

A thin bar of length L lies in the xy plane and carries linear charge density , where ranges from 0 to . Calculate the potential at the point on the y-axis.

**Possible Answers:**

**Correct answer:**

Use the linear charge density and length element , where each point is from the point . The potential is therefore

### Example Question #11 : Calculating Electric Potential

A uniformly charged ring of radius carries a total charge . Calculate the potential a distance from the center, on the axis of the ring.

**Possible Answers:**

**Correct answer:**

Use the linear charge density and length element . The distance from each point on the ring to the point on the axis is . Lastly, integrate over from to to obtain

### Example Question #181 : Ap Physics C

A uniformly charged square frame of side length carries a total charge . Calculate the potential at the center of the square.

You may wish to use the integral:

**Possible Answers:**

**Correct answer:**

Calculate the potential due to one side of the bar, and then multiply this by to get the total potential from all four sides. Orient the bar along the x-axis such that its endpoints are at , and use the linear charge density . The potential is therefore

### Example Question #1 : Understanding Charge Distributions On Objects

Consider a spherical shell with radius and charge . What is the magnitude of the electric field at the center of this spherical shell?

**Possible Answers:**

Zero

**Correct answer:**

Zero

According to the shell theorem, the total electric field at the center point of a charged spherical shell is always zero. At this point, any electric field lines will result in symmetry, canceling each other out and creating a net field of zero at that point.

### Example Question #1 : Interpreting Electric Charge Diagrams

A charge of unknown value is held in place far from other charges. Its electric field lines and some lines of electric equipotential (V_{1} and V_{2}) are shown in the diagram.

A second point charge, known to be negative, is placed at point A in the diagram. In which direction will the second, negative charge freely move?

**Possible Answers:**

Toward the original charge Q

It will remain stationary

Toward point A

Toward point C

**Correct answer:**

Toward point C

The original charge Q is negative, as indicated by the direction of the electric field lines in the diagram. A negative point charge of any value placed at point A will cause both charges to feel a mutually repelling force on each other. Therefore, the second charge will be repelled by the original negative charge with a force pointing radially along a line connecting the center of Q and the point A, resulting in free movement toward C. Additionally, point B is on a line of equipotential to point A; negative point charges will move from regions of lower electric potential to higher electric potential (against the direction of the electric field lines), so point B is not a viable answer.

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