Practice Final 1. If a = 3.0 mm, b = 4.0 mm, Q1 = 60 nC, Q2 = 80 nC, and q = 32 nC in the figure, what is the

magnitude of the total electric force on q?

a. 1.6 N b. 1.3 N c. 1.9 N d. 2.2 N e. 0.040 N

b

2. If Q = 20 µC and L = 60 cm, what is the magnitude of the electrostatic force on any one of the charges shown?

a. 25 N b. 19 N c. 15 N d. 9.1 N e. 14 N

d

3. Which one of the diagrams below is not a possible electric field configuration for a region of space which does not contain any charges?

d

4. Two imaginary spherical surfaces of radius R and 2R respectively surround a positive point charge Q located at the center of the concentric spheres. When compared to the number of field lines 1N going through the sphere of radius R, the number of electric field lines 2N going

through the sphere of radius 2R is

a. 124

1NN .

b. 122

1NN .

c. 12 NN .

d. 12 2NN .

e. 12 4NN .

c

5. An uncharged spherical conducting shell surrounds a charge –q at the center of the shell. Then charge q3 is placed on the outside of the shell. When static equilibrium is reached, the

charges on the inner and outer surfaces of the shell are respectively

a. qq , .

b. qq , .

c. qq 2 , .

d. qq ,2 .

e. 0 ,3q .

c

6. Two planes of charge with no thickness, A and B, are parallel and vertical. The electric

field in region I to the left of plane A has magnitude 3

20 and points to the left. The electric field

in the region to the right of B has magnitude 3

20 and points to the right. The electric field in

the region between the two planes has magnitude

20 and points to the right. The surface

charge density on planes A and B respectively is

a.

2, .

b.

2,

c. ,

2.

d. ,

2

e. 2 , .

e

7. A point charge of 6.0 nC is placed at the center of a hollow spherical conductor (inner radius = 1.0 cm, outer radius = 2.0 cm) which has a net charge of –4.0 nC. Determine the resulting charge density on the inner surface of the conducting sphere.

a. +4.8 µC/m2

b. –4.8 µC/m2

c. –9.5 µC/m2

d. +9.5 µC/m2

e. –8.0 µC/m2

b

8. A proton (m = 1.7 10–27 kg, q = +1.6 10–19 C) starts from rest at point A and has a speed of 40 km/s at point B. Only electric forces act on it during this motion. Determine the electric potential difference AB VV .

a. +8.5 V b. –8.5 V c. –4.8 V d. +4.8 V e. –17 V

b

9. You are told that E dA summed over the surface area of both sphere A and sphere B below

is equal to Q

0. You can conclude that

A B

a. Sphere A contains charge qin Q .

b. Sphere B contains charge qin Q .

c. Sphere B contains charge qin Q .

d. Each sphere contains charge qin Q

2.

e. The sum of the charges contained in both spheres is Q .

e

10. Which of the following represents the equipotential lines of a dipole?

e

11. Determine the charge stored by C1 when C1 = 20 µF, C2 = 10 µF,C3 = 30 µF, and V0 = 18 V.

a. 0.37 mC b. 0.24 mC c. 0.32 mC d. 0.40 mC e. 0.50 mC

b

12. Determine the equivalent capacitance of the combination shown when C = 12 nF.

a. 34 nF b. 17 nF c. 51 nF d. 68 nF e. 21 nF

b

13. A parallel plate capacitor is charged to voltage V and then disconnected from the battery. Leopold says that the voltage will decrease if the plates are pulled apart. Gerhardt says that the voltage will remain the same. Which one, if either, is correct, and why?

a. Gerhardt, because the maximum voltage is determined by the battery. b. Gerhardt, because the charge per unit area on the plates does not change. c. Leopold, because charge is transferred from one plate to the other when the plates

are separated. d. Leopold, because the force each plate exerts on the other decreases when the plates

are pulled apart. e. Neither, because the voltage increases when the plates are pulled apart.

e

14. A parallel plate capacitor of capacitance C0 has plates of area A with separation d

between them. When it is connected to a battery of voltage V0, it has charge of magnitude Q0 on

its plates. It is then disconnected from the battery and the plates are pulled apart to a separation 2d without discharging them. After the plates are 2d apart, the new capacitance and the potential difference between the plates are

a. 2

1C0,

2

1V0

b. 2

1C0, V0

c. 2

1C0, 2V0

d. C0, 2V0

e. 2C0, 2V0

c

15. A 15-µF capacitor is charged to 40 V and then connected across an initially uncharged 25-µF capacitor. What is the final potential difference across the 25-µF capacitor?

a. 12 V b. 18 V c. 15 V d. 21 V e. 24 V

c

16. The circuit below contains 5 light bulbs. The emf is 110 V. Which light bulb(s) is(are) brightest?

a. A: The one closest to the positive terminal of the battery. b. A and C: The bulbs closest to the positive terminal of the battery. c. A and B: Because they are closest to the terminals of the battery. d. C and D: Because they receive current from A and B and from E. e. E: Because the potential difference across E is that of the battery.

e

17. Determine the potential difference, VA – VB in the circuit segment shown below when I =

2.0 mA and Q = 50 µC.

a. –40 V b. +40 V c. +20 V d. –20 V e. –10 V

d

18. What is the equivalent resistance between points a and b when R = 13 ?

a. 29

b. 23

c. 26

d. 20

e. 4.6

d

19. An electron moves in a region where the magnetic field is uniform, has a magnitude of 60 µT, and points in the positive x direction. At t = 0 the electron has a velocity that has an x component of 30 km/s, a y component of 40 km/s, and a z component of zero. What is the pitch of the resulting helical path?

a. 13 mm b. 32 mm c. 24 mm d. 18 mm e. 3.8 mm

d

20. When the number of turns in a solenoid and its length are both doubled, the ratio of the magnitude of the new magnetic field inside to the magnitude of the original magnetic field inside is:

a. 0.25 b. 0.50 c. 1 d. 2 e. 4

c

21. Three coplanar parallel straight wires carry equal currents I as shown below. The current in the outer wires is directed to the right, and that in the middle wire is directed to the left. Each pair of wires is a distance a apart. The direction of the magnetic force on the middle wire

I

I

I

a. is up out of the plane of the wires. b. is down into the plane of the wires. c. is in the plane of the wires, directed upwards. d. is in the plane of the wires, directed downwards e. cannot be defined, because there is no magnetic force on the middle wire.

e

22. The segment of wire (total length = 6R) is formed into the shape shown and carries a current I. What is the magnitude of the resulting magnetic field at the point P?

a. R

Iµ

8

3 0

b. R

Iµ

2

3 0

c. R

Iµ

4

3 0

d. R

Iµ

2

3 0

e. R

Iµ

8

3 0

a

23. Coil 1, connected to a 100 resistor, sits inside coil 2. Coil 1 is connected to a source of 60 cycle per second AC current. Which statement about coil 2 is correct?

a. No current will be induced in coil 2. b. DC current (current flow in only one direction) will be induced in coil 2. c. AC current (current flow in alternating directions) will be induced in coil 2. d. DC current will be induced in coil 2, but its direction will depend on the initial

direction of flow of current in coil 1. e. Both AC and DC current will be induced in coil 2.

c

24. The point P lies along the perpendicular bisector of the line connecting two long straight wires S and T perpendicular to the page. A set of directions A through H is shown next to the diagram. When the two equal currents in the wires are directed up out of the page, the direction of the magnetic field at P is closest to the direction of

a. E. b. F. c. G. d. H. e. A.

a

25. A rectangular loop of wire, with dimensions shown in Figure, carries a current of 2 A and is placed in

a magnetic field of 0.8 T. The wire rotates in the magnetic field and at one point it is perpendicular to the

magnetic field. What is the magnitude of the torque acting on the wire?

A) 0 Nm

B) 1 Nm

C) 2 Nm

D) 4 Nm

b

26. A metal bar of mass m and length L is suspended from two conducting wires, as shown in the sketch

in Figure 22-9. A uniform magnetic field B points vertically downward. Choose the expression that best

describes the condition satisfied by the angle θ that the suspending wires make with the vertical when

the bar carries a current I.

A) tan θ = mg

BIL

B) tan θ = Bg

mIL

C) tan θ = mIL

Bg

D) tan θ = BIL

mg

d

27. A conducting rod whose length is 25 cm is placed on a U-shaped metal wire that has a resistance R of

8 Ω as shown in Figure. The wire and the rod are in the plane of the paper. A constant magnetic field of

strength 0.4 T is applied perpendicular and into the paper. An applied force moves the rod to the right

with a constant speed of 6 m/s. What is the magnitude of the induced emf in the wire?

A) 0.2 V

B) 0.4 V

C) 0.5 V

D) 0.6 V

d

28. A circular coil with 600 turns has a radius of 15 cm. The coil is rotating about an axis perpendicular to

a magnetic field of 0.020 T. If the maximum induced emf in the coil is 1.6 V, at what angular frequency is

the coil rotating?

A) 0.30 rad/s

B) 0.60 rad/s

C) 1.9 cycles/sec

D) 1.9 rad/s

d

29. At t = 0 the switch S is closed with the capacitor uncharged. If C = 40 µF, = 50 V, and R

= 5.0 k, how much energy is stored by the capacitor when I = 2.0 mA?

a. 20 mJ b. 28 mJ c. 32 mJ d. 36 mJ e. 40 mJ

c

30. A 1.50-H inductor is connected in series with a 200-Ω resistor through a 15.0-V dc power supply and

a switch. If the switch is closed at t = 0 s, what is the energy stored by the inductor 20.0 ms after the switch

is closed?

A) 0.910 mJ

B) 1.83 mJ

C) 3.65 mJ

D) 7.31 mJ

c

31. The primary coil of a transformer has 100 turns and its secondary coil has 400 turns. If the ac current

in the secondary coil is 2 A, what is the current in its primary coil?

A) 2 A

B) 8 A

C) 1/2 A

D) 4 A

b

32. A circular coil of copper wire is lying flat on a horizontal table. A bar magnet is held with its south

pole downward, vertically above the center of the coil. The magnet is released from rest and falls toward

the coil. As viewed from above, you can say that, as it falls, the magnet induces

A) counterclockwise current in the loop.

B) clockwise current in the loop.

C) mo current in the loop.

D) an emf but no electric current in the loop.

b

33. Two equal point charges of magnitude 4.0 µC are situated along the x-axis at x1 = -2.0 m and x2 = -2.0

m. What is the electric potential energy of this system of charges?

A) -36 mJ

B) 36 mJ

C) 0 J

D) 72 mJ

b

34. A uniform electric field with a magnitude of 8 × 106 N/C is applied to a cube of edge length 0.1 m as

shown in Figure. If the direction of the E-field is along the +x-axis, what is the electric flux passing

through the shaded face of the cube?

A) 0.8 × 104 Nm2/C

B) 8 × 104 Nm2/C

C) 80 × 104 Nm2/C

D) 800 × 104 Nm2/C

b

35. What is the potential difference Vb – Va shown in the circuit below.

a. –8.0 V

b. +8.0 V

c. –18 V

d. +18 V

e. –12 V

a