# AP Physics C Electricity : Understanding Electrostatics

## Example Questions

### Example Question #1 : Electricity And Magnetism Exam

A hollow metal sphere with a diameter of 10cm has a net charge of distributed uniformly across its surface. What is the magnitude of the field a distance 2.0m from the center of the sphere?       Explanation:

Relevant equations: (electric field of point charge)

Anywhere outside the metal sphere, the electric field is the same as it would be for a point charge of the same magnitude, located at the center of the sphere. So, calculate the electric field of a point charge given:   Plugging in gives: ### Example Question #1 : Electricity And Magnetism Exam

Two infinite parallel conducting sheets each have positive charge density . What is the magnitude and direction of the electric field to the right of the right sheet? , to the right , to the right , to the right  , to the left , to the right

Explanation:

Relevant equations: (field due to single infinite plane)

Electric field is additive; in other words, the total electric field from the two planes is the sum of their individual fields:   The direction of the electric field is away from positive source charges. Thus, to the right of these positively charged planes, the field points away to the right.

### Example Question #1 : Electricity

Consider a spherical capacitor made of two nested spheres. The smaller sphere has a radius of and a charge of , and lies within a larger sphere with radius and a charge of Which of the following equations accurately describes the capacitance of this spherical capacitor?  Due to symmetry, this scenario would not produce capacitance   Explanation:

To solve this problem, we will need to derive an equation.

We know that:  We can use Gauss's law to derive the electric field between the two circles yielding: Doing our integration with respect to from to , we get: We can plug this back into our equation for capacitance to get: ### All AP Physics C Electricity Resources 