PHYS2424 – SPRING 2000
EXAM #1 – PART 1
Electric Force, Fields, Potential, Capacitance, and Circuits
NAME ______
I. Basic Equation and Definitions ______(50 marks)
II. Multiple Choice ______(40 marks)
III. Short Problems ______(45 marks)
TOTAL PART 1 ______(135 marks)
TOTAL PART 2 ______(310 marks)
TOTAL POINTS ______
GRADE ______
I. Basic Equations and Definitions – ( 5 marks each)
1. Write Coulomb’s Law :
2. Definition of Electric Field
3. Definition of Electric Flux
4. Gauss’s Law
5. Mathematical formula used to find the electric potential difference if one knows the electric field.
6. The equation that defines capacitance
7. The definition of circuit elements in series
8. The definition of circuit elements in parallel
9. The definition of an open circuit
10. The definition of a short circuit
II. Multiple Choice ( 5 marks each)
1. Two small spherical charges repulse each other with a force “F” when placed a distance “d” apart. If the charge on each sphere is doubled, and the distance between them is doubled, then the new force of repulsion is:
A. F/2 B. F C. 2F
D. F/4 E. None of These
2. The conducting thick spherical shell shown below has a hollow, empty center and carries a total charge q.
The electric field will be zero at:
A. Point A only. B. Points A and B only.
C. Points A,B, and C only. D. Point D only.
E. None of These.
3. Compared to a single light bulb connected to a battery, two identical light bulbs connected in series with the same battery will use
A. more current. B. less current.
C. the same current. D. Not enough information given.
4. The cross-section of a charged, solid, metal sphere, existing under electrostatic
conditions, is shown in the figure below. The electrostatic potential difference is zero between points
A. A and B. B. A and C. C. D and E.
D. All of the above. E. None of these.
5. Circle the most probable trajectory for a negatively charged fluorine ion fired horizontally between the two charged capacitor plates shown below:
6. A point charge Q is placed in the center of a cube with sides of length A. The electric flux through the right face of the cube
A. B. C.
D. E. None of these.
7. Two identical conducting spheres, one with charge +3q and the other with charges
–q, are allowed to touch, and then they are separated. The force between the two
bodies before and after contact will be
A. repulsive before and attractive after contact.
B. repulsive before and after contact.
C. attractive before and after contact.
D. attractive before and repulsive after contact.
E. Attractive before contact, but no attraction or repulsive after contact.
8. What is the equivalent resistance between points A and B of the circuit shown below?
A. 12.4 ohms B. 1.93 ohms C. 5.00 ohms
D. 20.0 ohms F. None of these
III. Short Problems ( 15 marks each)
1. Draw and label the electric field lines and equipotential surfaces for the following charge distribution.
2. Starting from the definition of a parallel capacitance, show that the capacitance of
a parallel plate capacitor is given by the formula:
3. Show that the voltage drop across a coaxial cable with an inner conductor of radius A surrounded by an outer annular conductor of inner radius B is given by .