PHYSICS 2220 - PRACTICE EXAM #1
1. Two charges are placed at the bottom corners
of an equilateral triangle. What is the electric
field (unit vector notation) at the top corner,
point P?
2. An electron is placed at point P, and then
released. Find the acceleration (unit vector
notation) of the electron.
3. Two point charges of 2 µC and 5 µC are placed on the opposite
ends of a cord 50 cm long. What is the tension in the cord?
4. A solid conducting sphere has radius a and carries charge +Q.
It is inside a hollow conducting sphere of inner radius b and
outer radius c that carries a charge +Q. Find the electric field
for i) r < a; ii) a < r < b; iii) b < r < c; iv) r > c.
5. In problem 4, how much charge is on the inner surface of the
hollow sphere? On the outer surface of the hollow sphere?
6. A giant solid spherical conductor is the size of the Earth
(radius = 6.37 x 106 m). Just above its surface is a downward
electric field of 100 N/C. What is the charge per unit area on
the surface?
7. An electric field passes radially outward through the surface
of a sphere of radius 1.5 m. At the surface of the sphere the
electric field strength is 5000 N/C. What is the flux through
the surface of the sphere? Find the charge inside the sphere.
8. An electron is released from rest in an electric field of
2700 N/C. How much time passes before the electron reaches a
speed of 0.1 c, where c = speed of light = 3 x 108 m/s?
9. Four charges Q are at the corners of a square of side L. Find
the potential energy of the four charges, and find the electric
potential (voltage) at the center of the square.
10. Two large conducting plates are separated by 1.5 cm and have
a constant electric field of 400 N/C between them, directed
toward the left-hand plate. The left-hand plate is grounded, and
so has an electric potential of 0 V. What is the electric
potential of the right-hand plate?
