Question 1

The electric field just outside the surface of a hollow conducting sphere of radius 20 cm has a magnitude of 500 N/C and is directed outward. An unknown charge Q is introduced into the center of the sphere and it is noted that the electric field is still directed outward but has decreased to 100 N/C. What is the magnitude of the charge Q?

Accepted Answer

A)  1.5 nC 
B)  1.8 nC 
C)  1.3 nC 
D)  1.1 nC 
E)  2.7 nC

Question 2

Two identical particles, each with a mass of 4.5 μg and a charge of 30 nC, are moving directly toward each other with equal speeds of 4.0 m/s at an instant when the distance separating the two is equal to 25 cm. How far apart will they be when closest to one another?

Accepted Answer

A)  9.8 cm 
B)  12 cm 
C)  7.8 cm 
D)  15 cm 
E)  20 cm

Question 3

An infinite plane of charge with  is tilted at a 45° angle to the vertical direction as shown below. The potential difference, VB − VA, in volts, between points A and B, a 4.50 m distance apart, is

Accepted Answer

A)  −7.06. 
B)  −9.98. 
C)  −14.11. 
D)  +7.06. 
E)  +9.98.

Question 4

A charge of 10 nC is distributed uniformly along the x axis from x = −2 m to x = +3 m. Which of the following integrals is correct for the electric potential (relative to zero at infinity) at the point x = +5 m on the x axis?

Accepted Answer

A) 
 
B) 
 
C) 
 
D) 
 
E)

Question 5

A +4.0-μC charge is placed on the x axis at x = +3.0 m, and a −2.0-μC charge is located on the y axis at y = −1.0 m. Point A is on the y axis at y = +4.0 m. Determine the electric potential at point A (relative to zero at the origin).

Accepted Answer

A)  6.0 kV 
B)  8.4 kV 
C)  9.6 kV 
D)  4.8 kV 
E)  3.6 kV

Question 6

An electron (m = 9.1 × 10−31 kg, q = −1.6 × 10−19 C) starts from rest at point A and has a speed of 5.0 × 106 m/s at point B. Only electric forces act on it during this motion. Determine the electric potential difference VA − VB.

Accepted Answer

A)  −71 V 
B)  +71 V 
C)  −26 V 
D)  +26 V 
E)  −140 V

Question 7

Identical point charges (+30 μC) are placed at the corners of a rectangle (4.0 m × 6.0 m). How much external energy is required to bring a charge of 55 μC from infinity to the midpoint of one of the 6.0-m long sides of the rectangle?

Accepted Answer

A)  22 J 
B)  16 J 
C)  13 J 
D)  19 J 
E)  8.0 J

Question 8

The electric field in the region defined by the y-z plane and the positive x axis is given by E = ax, where a is a constant. (There is no field for negative values of x.) As x increases in magnitude, relative to V = 0 at the origin, the electric potential in the region defined above is

Accepted Answer

A)  a decreasing function proportional to −|x2|. 
B)  a decreasing function proportional to −|x|. 
C)  constant. 
D)  an increasing function proportional to +|x|. 
E)  an increasing function proportional to +|x2|.

Question 9

A particle (q = +5.0 μC) is released from rest when it is 2.0 m from a charged particle which is held at rest. After the positively charged particle has moved 1.0 m toward the fixed particle, it has a kinetic energy of 50 mJ. What is the charge on the fixed particle?

Accepted Answer

A)  −2.2 μC 
B)  +6.7 μC 
C)  −2.7 μC 
D)  +8.0 μC 
E)  −1.1 μC

Question 10

Equipotentials are lines along which

Accepted Answer

A)  the electric field is constant in magnitude and direction. 
B)  the electric charge is constant in magnitude and direction. 
C)  maximum work against electrical forces is required to move a charge at constant speed. 
D)  a charge may be moved at constant speed without work against electrical forces. 
E)  charges move by themselves.

Question 11

Two flat conductors are placed with their inner faces separated by 6.0 mm. If the surface charge density on one of the inner faces is 40 pC/m2, what is the magnitude of the electric potential differences between the two conductors?

Accepted Answer

A)  36 mV 
B)  18 mV 
C)  32 mV 
D)  27 mV 
E)  14 mV

Exam 25: Electric Potential

Two identical particles, each with a mass of 4.5 μg and a charge of 30 nC, are moving directly toward each other with equal speeds of 4.0 m/s at an instant when the distance separating the two is equal to 25 cm. How far apart will they be when closest to one another?

An infinite plane of charge with is tilted at a 45° angle to the vertical direction as shown below. The potential difference, V_B − V_A, in volts, between points A and B, a 4.50 m distance apart, is

A charge of 10 nC is distributed uniformly along the x axis from x = −2 m to x = +3 m. Which of the following integrals is correct for the electric potential (relative to zero at infinity) at the point x = +5 m on the x axis?

A +4.0-μC charge is placed on the x axis at x = +3.0 m, and a −2.0-μC charge is located on the y axis at y = −1.0 m. Point A is on the y axis at y = +4.0 m. Determine the electric potential at point A (relative to zero at the origin) .

An electron (m = 9.1 × 10−³¹ kg, q = −1.6 × 10−¹⁹ C) starts from rest at point A and has a speed of 5.0 × 10⁶ m/s at point B. Only electric forces act on it during this motion. Determine the electric potential difference V_A − V_B.

Identical point charges (+30 μC) are placed at the corners of a rectangle (4.0 m × 6.0 m) . How much external energy is required to bring a charge of 55 μC from infinity to the midpoint of one of the 6.0-m long sides of the rectangle?

The electric field in the region defined by the y-z plane and the positive x axis is given by E = ax, where a is a constant. (There is no field for negative values of x.) As x increases in magnitude, relative to V = 0 at the origin, the electric potential in the region defined above is

A particle (q = +5.0 μC) is released from rest when it is 2.0 m from a charged particle which is held at rest. After the positively charged particle has moved 1.0 m toward the fixed particle, it has a kinetic energy of 50 mJ. What is the charge on the fixed particle?

Equipotentials are lines along which

Two flat conductors are placed with their inner faces separated by 6.0 mm. If the surface charge density on one of the inner faces is 40 pC/m², what is the magnitude of the electric potential differences between the two conductors?