HW 4.2 Physics multiple choice (Magnetism)

Which statement regarding the force of a magnetic field on a current-carrying wire is true? a. All of the above statements are false. b. The force on the wire is directed parallel to both the wire and the magnetic field. c. The magnetic force on the wire is independent of the direction of the current. d. The force takes its largest value when the magnetic field is parallel to the wire.

a. All of the above statements are false.

There is a current I flowing in a clockwise direction in a square loop of wire that is in the plane of the paper. If the magnetic field B is toward the right, and if each side of the loop has length L, then the net magnetic torque acting on the loop is: a. IBL^2. b. ILB. c. 2ILB. d. zero.

a. IBL^2.

When an electromagnet has an iron core inserted, what happens to the strength of the magnet? a. It increases. b. It remains the same. c. It decreases. d. Since it depends on the metal used in the wires of the electromagnet, any of the above.

a. It increases.

A circular current loop is placed in an external magnetic field. How is the torque related to the radius of the loop? a. directly proportional to radius squared b. directly proportional to radius c. inversely proportional to radius d. inversely proportional to radius squared

a. directly proportional to radius squared

Consider two long, straight parallel wires, each carrying a current I. If the currents are flowing in opposite directions: a. the two wires will repel each other. b. neither wire will exert a force on the other. c. the two wires will exert a torque on each other. d. the two wires will attract each other.

a. the two wires will repel each other.

The current in a long wire creates a magnetic field in the region around the wire. How is the strength of the field at distance r from the wire center related to the magnitude of the field? a. field directly proportional to r b. field inversely proportional to r c. field inversely proportional to r2 d. field directly proportional to r2

b. field inversely proportional to r

A square loop of wire has a current going around it. The magnetic field from the current on each side of the loop results in a magnetic force on the wire on the opposite side. Each resulting magnetic force on the opposite side wire: a. depends on whether the current is clockwise of counterclockwise. b. pushes outward on the loop. c. pushes inward on the loop. d. is actually zero since a current cannot push on itself.

b. pushes outward on the loop.

A current in a solenoid coil creates a magnetic field inside that coil. The field strength is directly proportional to: a. the coil area. b. the current. c. Both A and B are valid choices. d. None of the above choices are valid.

b. the current.

Two long parallel wires 10.0 cm apart carry currents of 3.0 A and 2.9 A in the same direction. Is there any point between the two wires where the magnetic field is a. yes, 5.1 cm from the 2.9-A wire b. yes, 5.1 cm from the 3.0-A wire c. yes, 4.9 cm from the 3.0-A wire d. no. e. yes, midway between the wires

b. yes, 5.1 cm from the 3.0-A wire

A current-carrying wire of length 52.0 cm is positioned perpendicular to a uniform magnetic field. If the current is 15.0 A and it is determined that there is a resultant force of 2.3 N on the wire due to the interaction of the current and field, what is the magnetic field strength? b. 0.020 T c. 0.29 T d. 0.18 T e. 0.38 T

c. 0.29 T

A solenoid with 568 turns, 0.19 m long, carrying a current of 3.5 A and with a radius of 10 −2 m will have what strength magnetic field at its center? (magnetic permeability in empty space µ 0 = 4 π × 10 −7 T ⋅m/A) a. ​4.1E-2 T b. 3.3E-3 T c. 1.3E-2 T d. 1.2E-1 T e. 2.5E-3 T

c. 1.3E-2 T

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? a. 6.2E-4 A b. 4.2E+2 A c. 5.4E-3 A d. 8.8E-5 A e. 1.5E+0 A

c. 5.4E-3 A

The direction of the force on a current carrying wire located in an external magnetic field is which of the following? a. perpendicular to the current b. perpendicular to the field c. Both choices A and B are valid. d. None of the above are valid.

c. Both choices A and B are valid.

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

c. Both have the same magnetic field.

The force exerted on a current-carrying wire located in an external magnetic field is directly proportional to which of the following? a. current strength b. field strength c. both A and B d. None of the above are valid.

c. both A and B

Four long wires are perpendicular to the x-y plane. Each wire carries the same magnitude current. Wire 1 goes through point (a, a, 0) on the x-y plane, wire 2 goes through the point (-a, a, 0), wire 3 goes through the point (-a, -a, 0), and wire 4 goes through the point (a, -a, 0). Wires 1 and 2 carry their currents in the positive z direction and wires 3 and 4 carry their currents in the - z direction. What is the direction of the resulting magnetic field at the origin? a. the -x direction b. the -y direction c. the +x direction d. There is no direction since the field is zero at this position.

c. the +x direction

There is a current I flowing in a clockwise direction in a square loop of wire that is in the plane of the paper. If the magnetic field B is toward the right, and if each side of the loop has length L, then the net magnetic force acting on the loop is: a. ILB. b. 2ILB. c. zero. d. IBL2

c. zero.

A copper wire of length 25.0 cm is in a magnetic field of 0.36 T. If it has a mass of 11.0 g, what is the minimum current through the wire that would cause a magnetic force equal to its weight? a. 3.3 A b. 0.48 A c. 0.75 A d. 1.2 A e. 12 A

d. 1.2 A

Two long parallel wires 45.6 cm apart are carrying currents of 13.0 A and 23.0 A in the same direction. What is the magnitude of the magnetic field halfway between the wires? a. 3.16E-5 T b. 2.02E-5 T c. 1.14E-5 T d. 8.77E-6 T e. 4.39E-6 T

d. 8.77E-6 T

A current in a long, straight wire produces a magnetic field. The magnetic field lines: a. form circles that pass through the wire. b. go out from the wire to infinity. c. come in from infinity to the wire. d. form circles that go around the wire.

d. form circles that go around the wire.

Two parallel conductors each of 0.34 m length, separated by 6.4 × 10 −3 m and carrying 4.8 A in opposite directions, will experience what type and magnitude of mutual force? (magnetic permeability in empty space µ 0 = 4 π × 10 −7 T ⋅m/A) a. attractive, 2.1E-3 N b. repulsive, 2.1E-3 N c. attractive, 2.4E-4 N d. repulsive, 2.4E-4 N e. zero

d. repulsive, 2.4E-4 N

Two parallel wires are separated by 0.25 m. Wire A carries 5.0 A and Wire B carries 10 A, both currents in the same direction. The force on 0.80 m of Wire A is: a. away from Wire B. b. half that on 0.80 m of wire B. c. one-fourth that on 0.80 m of wire B. d. toward Wire B.

d. toward Wire B