Homework Answers

A parallel-plate air capacitor is to store charge of magnitude 240.0 pC on each plate when the

potential difference between the plates is 42.0 V. (a) If the area of each plate is 6.80 cm2

, what is

the separation between the plates? (b) If the separation between the two plates is double the value

calculated in part (a), what potential difference is required for the capacitor to store charge of

magnitude 240.0 pC on each plate?

The plates of a parallel-plate capacitor are 2.50 mm apart, and each carries a charge of

magnitude 80.0 nC. The plates are in vacuum. The electric field between the plates has a magnitude

of 4.00 X 106 V/m(a) What is the potential difference between the plates? (b) What is the area of

each plate? (c) What is the capacitance?

A thin spherical shell with radius R1 = 3.00 cm is concentric with a larger thin spherical shell

with radius R2 = 5.00 cm. Both shells are made of insulating material. The smaller shell has

charge q1 = +6.00 nC distributed uniformly over its surface, and the larger shell has charge

q2 = - 9.00 nC distributed uniformly over its surface. Take the electric potential to be zero at an

infinite distance from both shells. (a) What is the electric potential due to the two shells at the

following distance from their common center: (i) r = 0; (ii) r = 4.00 cm ; (iii) r = 6.00 cm? (b) What

is the magnitude of the potential difference between the surfaces of the two shells? Which shell is

at higher potential: the inner shell or the outer shell?

A small particle has charge – 5.00 µC and mass 2.00 X 10-4 kg. It moves from point A, where

the electric potential is VA = +2.00 V, to point B, where the electric potential is VB = +8.00 V. The

electric force is the only force acting on the particle. The particle has speed 5.00 m/s at point A.

What is its speed at point B? Is it moving faster or slower at B than at A? Explain.

A point charge q1 = +2.40 µC is held stationary at the origin. A second point charge

q2 = - 4.30 µC moves from the point x = 0.150 m, y = 0 to the point x = 0.250 m, y = 0.250 m.

How much work is done by the electric force on q2.

A small sphere with a mass of of 4.00 X 10-6 kg and carrying a charge of 5.00 X 10-8 C hangs

from a thread near a very large, charged insulating sheet, as shown below. The charge density on

the surface of the sheet is uniform and equal to 2.50 X 10-9 C/m2

. Find the angle of the thread.

A very long uniform line of charge has charge per unit length 4.80 µC/m and lies along the x￾axis. A second long uniform line of charge has charge per unit length – 2.40 µC/m and is parallel

to the -axis at y = 0.400m. What is the net electric field (magnitude and direction) at the following

points on the y-axis: (a) y = 0.200 m and (b) y = 0.600 m?

A 6.20 μC point charge is at the center of a cube with sides of length 0.500 m. (a) What is the

electric flux through one of the six faces of the cube? (b) How would your answer to part (a)

change if the sides were 0.250 m long? Explain