Question 1

An electron moves through a region of crossed electric and magnetic fields.The electric field E = 2 300 V/m and is directed straight down.The magnetic field B = 0.95 T and is directed to the left.For what velocity v of the electron into the paper will the electric force exactly cancel the magnetic force?

Accepted Answer

A) 2 400 m/s 
B) 2 200 m/s 
C) 3 500 m/s 
D) 4 400 m/s 
E) 3 800 m/s

Question 2

A rectangular coil (0.13 m × 0.98 m)has 277 turns and is in a uniform magnetic field of 0.50 T.If the orientation of the coil is varied through all possible positions,the maximum torque on the coil by magnetic forces is 0.096 N⋅m.What is the current in the coil?

Accepted Answer

A) 6.2E-4 A 
B) 1.5E+0 A 
C) 5.4E-3 A 
D) 4.2E+2 A 
E) 8.8E-5 A

Question 3

If an electron is released at the equator and falls toward the Earth under the influence of gravity,the magnetic force on the electron will be toward the:

Accepted Answer

A) south. 
B) east. 
C) west. 
D) north.

Question 4

The force exerted on a current-carrying wire located in an external magnetic field is directly proportional to which of the following?

Accepted Answer

A) current strength 
B) field strength 
C) both A and B 
D) None of the above are valid.

Question 5

A proton and a deuteron are moving with equal velocities perpendicular to a uniform magnetic field.A deuteron has the same charge as the proton but has twice its mass.The ratio of the magnetic force on the proton to that on the deuteron is:

Accepted Answer

A) 0.5. 
B) 1. 
C) 2. 
D) There is no magnetic force in this case.

Question 6

The path of a charged particle moving parallel to a uniform magnetic field will be a

Accepted Answer

A) straight line. 
B) circle. 
C) ellipse. 
D) parabola.

Question 7

Solenoid №1 has a length L,cross-sectional area A,and N turns.Solenoid №2 has a length 2L,cross-sectional area 2A,and 2N turns.Which solenoid has the greater magnetic field at its center when equal currents are going through them?

Accepted Answer

A) №1 
B) №2 
C) Both have the same magnetic field. 
D) Since it depends on the values of A and L,none of the above are correct.

Question 8

A proton moving at a speed of 4.2 × 106 m/s cuts across the lines of a magnetic field at an angle of 78°.The strength of the field is 0.91 × 10−4 T.What is the magnitude of the force acting on the proton? (qp = 1.6 × 10−19 C)

Accepted Answer

A) 1.3E-17 N 
B) 3.1E-17 N 
C) 6.0E-17 N 
D) 7.2E-9 N 
E) ​9.6E-36 N

Question 9

A high-voltage power line 23.0 m above the ground carries a current of 2 200 A.What is the magnetic field due to the current directly underneath the power line? (µ0 = 4π × 10−7 T⋅m/A)

Accepted Answer

A) 19.1 µT 
B) 60.1 µT 
C) 60.9 mT 
D) 12.0 mT 
E) 12.0 T

Question 10

A superconducting solenoid is to be designed to generate a magnetic field of 3.50 T.If the solenoid winding has 984 turns/m,what is the required current? (µ0 = 4π × 10−7 T⋅m/A)

Accepted Answer

A) 1.4E+3 A 
B) 9.0E+2 A 
C) 2.8E+3 A 
D) 4.5E+2 A 
E) 2.3E+2 A

Question 11

A horizontal wire of length 4.5 m carries a current of 5.8 A and is oriented so that the current direction is 53° S of W.The Earth's magnetic field is due north at this point and has a strength of 0.14 × 10−4 T.What is the size of the force on the wire?

Accepted Answer

A) 2.9E-4 N 
B) 3.4E-4 N 
C) 1.4E-4 N 
D) 2.2E-4 N 
E) 7.8E-5 N

Question 12

A soft magnetic material has which property?

Accepted Answer

A) It cannot be magnetized. 
B) It is easy to magnetize. 
C) It is hard to magnetize. 
D) It attracts slowly moving charges.

Question 13

A circular loop carrying a current of 1.6 A is oriented in a magnetic field of 0.30 T.The loop has an area of 0.14 m2 and is mounted on an axis,perpendicular to the magnetic field,which allows the loop to rotate.What is the torque on the loop when its plane is oriented at a 21° angle to the field?

Accepted Answer

A) 2.4E-2 N⋅m 
B) 6.3E-2 N⋅m 
C) 3.7E-2 N⋅m 
D) 5.6E-2 N⋅m 
E) 9.4E-1 N⋅m

Question 14

Assume that a uniform magnetic field is directed into this page.If an electron is released with an initial velocity directed from the bottom edge to the top edge of the page,which of the following describes the direction of the resultant force acting on the electron?

Accepted Answer

A) out of the page 
B) to the right 
C) to the left 
D) into the page

Question 15

If a proton is released at the equator and falls toward the Earth under the influence of gravity,the magnetic force on the proton will be toward the:

Accepted Answer

A) north. 
B) south. 
C) east. 
D) west.

Question 16

Square coil A has 2N turns and sides of length L,and square coil B has N turns and sides of length 2L.When a current of 2 amps is sent through coil A and a current of 1 amp is sent through coil B,which coil has the greater magnetic moment?

Accepted Answer

A) coil A 
B) coil B 
C) Both have the same magnetic moment. 
D) More information is needed.

Question 17

Two long parallel wires are a distance d apart.The current in one wire is 10 A and the current in the other wire is 30 A.The currents are in the same direction.If the 30-A current is increased to 50 A,by what factor does the magnitude of the magnetic field midway between the wires change?

Accepted Answer

A) 2 
B) 4 
C) 25/9 
D) 5/3

Question 18

Which of the following is not a hard magnetic material?

Accepted Answer

A) iron 
B) cobalt 
C) nickel 
D) both b and c

Question 19

The magnetic force on a charged particle moving at a constant speed in a uniform magnetic field will be doubled when the angle between the velocity of the particle and the direction of the magnetic field changes from 25.0° to

Accepted Answer

A) 57.7°. 
B) 12.5°. 
C) 12.2°. 
D) 50.0°.

Question 20

Two parallel wires carry a current I in the same direction.Midway between these wires is a third wire,also parallel to the other two,which carries a current 0.5 I,but in the direction opposite from the first two wires.In which direction are the net forces on the outer wires?

Accepted Answer

A) Since the net forces are zero,there is no direction. 
B) Both forces are toward the center wire. 
C) Both forces are away from the center wire. 
D) Both forces on the two wires are in the same direction in space.

Exam 19: Magnetism

A rectangular coil (0.13 m × 0.98 m) has 277 turns and is in a uniform magnetic field of 0.50 T.If the orientation of the coil is varied through all possible positions,the maximum torque on the coil by magnetic forces is 0.096 N⋅m.What is the current in the coil?