Physics/ answers to questions

1. Which one of the following statements best explains why it is
possible to define an electrostatic potential in a region of space that
contains an electrostatic field?

Work must be done to bring two positive charges closer together

Like charges repel one another and unlike charges attract one another

A positive charge will gain kinetic energy as it approaches a negative
charge

The work required to bring two charges together is independent of the
path taken

A negative charge will gain kinetic energy as it moves away from another
negative charge

2. Two positive point charges are separated by a distance R. If the
distance between the charges is reduced to R/2, what happens to the
total electric potential energy of the system?

It is doubled.

It remains the same.

It increases by a factor of 4.

It is reduced to one-half of its original value

It is reduced to one-fourth of its original value

3. Two point charges are arranged along the x axis as shown the figure.
At which of the following values of x is the electric potential equal to
zero? Note: At infinity, the electric potential is zero.

+0.05 m

+0.29 m

+0.40 m

+0.54 m

+0.71 m

4. If the work required to move a +0.35 C charge from point A to point B
is +125 J, what is the potential difference between the two points?

Zero volts

44 V

88 V

180 V

360 V

5. A charge is located at the center of sphere A (radius RA = 0.0010 m),
which is in the center of sphere B (radius RB = 0.0012 m). Spheres A and
B are both equipotential surfaces. What is the ratio VA/VB for the
potentials of these surfaces?

0.42

0.83

1.2

1.4

2.4

6. A parallel plate capacitor has a potential difference between its
plates of 1.2 V and a plate separation distance of 2.0 mm. What is the
magnitude of the electric field if a material that has a dielectric
constant of 3.3 is inserted between the plates?

75 V/m

180 V/m

250 V/m

400 V/m

500 V/m

Test 2

7. How many electrons flow through a battery that delivers a current of
3.0 A for 12 s?

4

36

4.8 Ч 1015

6.4 Ч 1018

2.2 × 1020

8. Which one of the following statements concerning superconductors is
false?

Below is critical temperature, the resistivity of a superconductor is
zero Ω-m.

Critical temperatures for some superconductors exceed 100 K.

All materials are superconducting at temperatures near absolute zero
kelvin

A constant current can be maintained in a superconducting ring for
several years without an emf.

Superconductors are perfect conductors

πt). What is the rms current for this circuit?

17.7 A

12.5 A

85.7 A

25.0 A

8.85 A

10. Some light bulbs are connected in parallel to a 120 V source as
shown in the figure. Each bulb dissipates an average power of 60 W. The
circuit has a fuse F that burns out when the current in the circuit
exceeds 9 A. Determine the largest number of bulbs, which can be used in
this circuit without burning out the fuse.

9

17

25

34

36

Ω. Determine the terminal voltage when the current drawn from the
battery is 1.0 A.

5.0 V

6.0 V

5.4 V

6.66 V

5.8 V

12. Three parallel plate capacitors, each having a capacitance of 1.0
μF are connected in parallel. The potential difference across the
combination is 100 V. What is the charge on any one of the capacitors?

30 μC

100 μC

300 μC

1000 μC

3000 μC

13. An uncharged 5.0-μF capacitor and a resistor are connected in
series to a 12-V battery and an open switch to form a simple RC circuit.
The switch is closed at t = 0 s. The time constant of the circuit is 4.0
s. Determine the maximum charge on the capacitor.

6.0 Ч 10–5 C

9.5 Ч 10–5 C

1.5 Ч 10–5 C

4.8 Ч 10–5 C

5.5 Ч 10–5 C

14. A proton traveling due east in a region that contains only a
magnetic field experiences a vertically upward force away from the
surface of the earth. What is the direction of the magnetic field?

North

East

South

West

Down

15. An electron traveling horizontally enters a region where a uniform
magnetic field is directed into the plane of the paper as shown. Which
one of the following phrases most accurately describes the motion of the
electron once it has entered the field?

upward and parabolic

upward and circular

downward and circular

upward, along a straight line

downward and parabolic

16. A loop of wire with a weight of 1.47 N is oriented vertically and
carries a current I = 1.75 A. A segment of the wire passes through a
magnetic field directed into the plane of the page as shown. The net
force on the wire is measured using a balance and found to be zero. What
is the magnitude of the magnetic field?



Zero tesla

0.51 T

0.84 T

1.5 T

4.2 T

17. A current-carrying, rectangular coil of wire is placed in a magnetic
field. The magnitude of the torque on the coil is not dependent upon
which one of the following quantities?

The magnitude of the current in the loop

The direction of the current in the loop

The length of the sides of the loop

The area of the loop

The orientation of the loop

18. A solenoid of length 0.250 m and radius 0.0200 m is comprised of 120
turns of wire. Determine the magnitude of the magnetic field at the
center of the solenoid when it carries a current of 15.0 A.

2.26 Ч 10–3 T

4.52 Ч 10–3 T

9.05 Ч 10–3 T

7.50 Ч 10–3 T

zero tesla

19. Which one of the following materials is not ferromagnetic?

Iron

Chromium dioxide

Nickel

Aluminum

Cobalt

20. A conducting loop of wire is placed in a magnetic filed that is
normal to the plane of the loop. Which one of the following actions will
not result in an induced current in the loop?

Rotate the loop about an axis that is parallel to the field and passes
through the center of the loop.

Increase the strength of the magnetic field.

Decrease the area of the loop.

Decrease the strength of the magnetic field.

Rotate the loop about an axis that is perpendicular to the field and
passes through the center of the loop.

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☊଀⑆㜀$␸䠀$摧ᚴÚ 㜀$␸䠀$摧ᚴÚ᠀21. The Earth’s
magnetic field passes through a square tabletop with a magnitude of 4.95
Ч 10–5 T and directed at an angle of 165° relative to the normal of
the tabletop. If the tabletop has 1.50-m sides, what is the magnitude of
the magnetic flux through it?

108 Ч 10–4 Wb

7.11 Ч 10–5 Wb

2.88 Ч 10–5 Wb

1.92 Ч 10–5 Wb

3.30 Ч 10–6 Wb

22. A long, straight wire is in the same plane as a rectangular,
conducting loop. The wire carries a constant current I as shown in the
figure. Which one of the following statements is true if the wire is
suddenly moved toward the loop?



There will be no induced emf and no induced current.

There will be an induced emf, but no induced current

There will be an induced current that is clockwise around the loop.

There will be an induced current that is counterclockwise around the
loop

There will be an induced electric field that is clockwise around the
loop.

23. The angular speed of a motor is 262 rad/s. The back emf generated by
the motor is 89.4 V. Assuming all other factors remain the same,
determine the back emf if the angular speed of the motor is reduced to
154 rad/s.

32.3 V

44.7 V

52.5 V

89.4 V

152 V

24. Determine the energy stored in a 95-mH inductor that carries a 1.4-A
current.

0.38 J

0.27 j

0.19 j

0.093 j

0.066 j

25. A transformer changes 120 V across the primary to 1200 V across the
secondary. If the secondary coil has 800 turns, how many turns does the
primary coil have?

40

80

100

400

4000