N m/C C/N m

or micro means p or pico means

1. E is always parallel to an equipotential surface.
2. E is always perpendicular to an equipotential surface.
3. E may pass through an equipotential surface at various angles, depending on the geometry.
4. In equilibrium, E is always zero inside a conductor.
5. In equilibrium E is guaranteed to be equal to zero only inside a spherically-symmetric conductor.
6. In equilibrium, the value of E inside a conductor depends on the boundary conditions.
7. In equilibrium, E always enters a conductor parallel to the surface.
8. In equilibrium, E always enters a conductor perpendicular to the surface.
9. In equilibrium, E may enter a conductor at any angle to the surface, depending on the surrounding charges.
10. Electric field lines never cross.
11. Electric field lines may cross when there is a nonuniform distribution of charge.

2. (5) A point charge is surrounded by a conductor in the form of a spherically symmetric shell.The net charge on the conductor is

(a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)

(i) zero

(j) none of the above

3. (5) An electron has a charge of C and a mass of

kg. In a particular television set, electrons are accelerated by a potential difference of 20 000 volts, starting from rest. What is the final speed of one of these electrons?

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4. (5) Two protons are placed apart and released from rest. Each has a charge of C and a mass of kg. What is the total kinetic energy of these two protons when they are very far apart?

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5. (5) A capacitor might be used in which of the following? (Circle all correct answers.)

1. a tuner for a radio
2. a camera's electronic flash attachment
3. a heart defibrillator
4. a computer keyboard
5. random access memory in a computer
6. none of the above

 

6. (5) A charge of 500 C is placed at the center of a cube which has a surface area of 6 m

. What is the total electric flux through the surface of the cube?

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7. (5) Three charges are placed at three of the corners of a square with an edge of 1 m. Each of them has a magnitude of 5.0C. What is the force on the middle charge, due to the other two charges which are diagonally opposite each other?

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8. (5) A parallel plate capacitor is charged up by a battery. The battery is then disconnected, but the charge remains on the plates. The plates are then pulled apart. State whether each of the following quantities increases decreases, or remains the same as the distance between the plates increases. Put the phrase "increases", "decreases", or "remains the same" to the right of each quantity.

1. capacitance of the capacitor ___________________________________
2. potential difference between the plates ___________________________________
3. electric field between the plates ___________________________________
4. electric potential energy stored by the capacitor ___________________________________

9. (5) An electric field of 150 000 N/C points due north at a certain spot. What are the magnitude and direction of the force that acts on a charge of -12.0 C at this spot?

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10. (5) When you walk across a rug on a dry day, your body can become electrified, and its electric potential can change. When the potential becomes large enough, a spark of negative charge can jump between your hand and a metal surface. A spark occurs when the electric field strength created by the charges on your body reaches the dielectric strength of the air. The dielectric strength of the air is N/C and is the electric field strength at which the air suffers dielectric breakdown. Suppose that a spark 2.5 mm long jumps between your hand and a metal doorknob. Assuming that the electric field is uniform, find the potential difference between your hand and the doorknob.

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11. (10 points, partial credit, show all work) A charge of +12C is 2 m from a charge of +4C. Let be the distance of a point from the 4C charge. For what value or values of will the electric field be equal to zero?

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12. (10 points, partial credit, show all work) A 12 volt battery is used to charge a parallel-plate capacitor. Then it is disconnected, leaving the plates of the capacitor charged. Finally, a material with a dielectric constant of 4.5 is placed between the plates. What is the final potential difference across the plates?

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13. (10 points, partial credit, show all work) A small object, which has a charge of C and a mass kg, is placed in a constant electric field. Starting from rest, the object accelerates to a speed of m/s in a time of s. Determine the magnitude of the electric field.

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14. (20 points, partial credit, show all work) Consider three charges , , and

.

= +5.0 C is at the origin.

= -10.0C is to the right of the origin by 0.10 m.

= -40.0 C is directly above the origin by 0.15 m.

Calculate the magnitude and direction of the total electrostatic force on .

Answers: Magnitude of total force is _________________________________

Direction of total force is _________________________________

[Give a precise specification of the direction.]