Question 1

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?

Accepted Answer

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.

Question 2

A proton and an alpha particle are moving perpendicular to a uniform magnetic field with the same speeds.If the velocity of the proton is at an angle of 20° with respect to the magnetic field direction,at what angle to the magnetic field direction would the alpha particle be moving if it experiences the same magnitude magnetic force as the proton? The alpha particle has 4 times the mass of the proton and twice its charge.

Accepted Answer

A)  10° 
B)  62° 
C)  43° 
D)  9.8°

Question 3

Two parallel wires are separated by 0.25 m.Wire A carries 4.1 A and Wire B carries 10 A,both currents in the same direction.The magnetic permeability in empty space µ0 = 4π × 10−7 T⋅m/A.The magnitude of the force on 1.4 m of Wire A is:

Accepted Answer

A)  2.6 × 10-5 N. 
B)  4.6 × 10-5 N. 
C)  less than 1.0 × 10-5 N. 
D)  3.2 × 10-5 N.

Question 4

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 5

A proton,which moves perpendicular to a magnetic field of 0.60 T in a circular path of radius 0.080 m,has what speed? (qp = 1.6 × 10−19 C and mp = 1.67 × 10−27 kg)

Accepted Answer

A)  9.2 × 106 m/s 
B)  4.6 × 106 m/s 
C)  9.6 × 106 m/s 
D)  3.4 × 106 m/s

Question 6

A superconducting wire carries a current of 104 A.Find the magnetic field at a distance of 0.25 m from the wire.(µ0 = 4π × 10−7 T⋅m/A)

Accepted Answer

A)  1.6 × 10−2 T 
B)  2 × 10−3 T 
C)  8 × 10−3 T 
D)  3.2 × 10−2 T

Question 7

Which of the following devices makes use of an electromagnet?

Accepted Answer

A)  relay 
B)  motor 
C)  both A and B 
D)  None of the above.

Question 8

A high-voltage power line 20 m above the ground carries a current of 5000 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)  14 mT 
B)  35 µT 
C)  20 µT 
D)  50 µT

Question 9

A copper wire of length 10 cm is in a magnetic field of 0.30 T.If it has a mass of 20 g,what minimum current through the wire would cause a magnetic force equal to its weight?

Accepted Answer

A)  4.9 A 
B)  6.5 A 
C)  2.0 A 
D)  1.3 A

Question 10

The magnetic domains in a magnetized piece of iron are characterized by which orientation?

Accepted Answer

A)  anti-parallel (opposite direction)to the magnetic axis 
B)  perpendicular to the magnetic axis 
C)  parallel to the magnetic axis 
D)  random

Question 11

A 2.0-m wire segment carrying a current of 0.60 A oriented parallel to a uniform magnetic field of 0.25 T experiences a force of what magnitude?

Accepted Answer

A)  0.30 N 
B)  6.7 N 
C)  0.15 N 
D)  zero

Question 12

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 13

Two long parallel wires 15 cm apart carry currents of 5.0 A and 8.0 A in the same direction.Is there any point between the two wires where the magnetic field is zero?

Accepted Answer

A)  yes,midway between the wires 
B)  yes,9.2 cm from the 5 A wire 
C)  no 
D)  yes,5.8 cm from the 5 A wire

Question 14

At the Fermilab accelerator in Weston,Illinois,singly-charged ions with momentum 3.2 × 10−16 kg⋅m/s are held in a circular orbit of radius 1 km by an upward magnetic field.What B-field must be used to maintain the ions in this orbit? (qion = 1.6 × 10−19 C)

Accepted Answer

A)  4 T 
B)  2 T 
C)  1 T 
D)  3 T

Question 15

Superconductors can carry very large currents with no resistance.If a superconducting wire is formed into a solenoid of length 50.0 cm with 250 turns,what is the magnetic field inside the solenoid when the current is 104 A? (µ0 = 4π × 10−7 T⋅m/A)

Accepted Answer

A)  12.6 T 
B)  2.50 T 
C)  1.25 T 
D)  6.28 T

Question 16

A proton moving with a speed of 6.0 × 105 m/s perpendicular to a uniform magnetic field of 0.20 T will follow which of the paths described below? (qp = 1.6 × 10−19 C and mp = 1.67 × 10−27 kg)

Accepted Answer

A)  a circular path of 1.6-cm radius 
B)  a circular path of 3.1-cm radius 
C)  a circular path of 6.3-cm radius 
D)  a straight line path

Question 17

A proton is released such that it has an initial speed of 5.0 × 105 m/s from left to right across the page.A magnetic field of 1.2 T is present at an angle of 30° to the horizontal direction (or positive x axis).What is the magnitude of the force experienced by the proton? (qp = 1.6 × 10−19 C)

Accepted Answer

A)  3.8 × 10−14 N 
B)  7.5 × 103 N 
C)  4.8 × 10−14 N 
D)  1.3 × 10−19 N

Question 18

A bar magnet is attached solidly to a frictionless surface and its length is aligned with the x axis.To the right of the first magnet a short distance away is a second bar magnet with its center placed on the x axis and its length perpendicular to the x axis.The second magnet is free to move.Once placed in position at rest,which best describes the initial motion of the second magnet?

Accepted Answer

A)  The magnet will move away from the fixed magnet. 
B)  The magnet will not move. 
C)  The magnet will move toward the fixed magnet. 
D)  The magnet will start to rotate.

Question 19

Niobium metal becomes a superconductor (with electrical resistance equal to zero)when cooled below 9 K.If superconductivity is destroyed when the surface magnetic field exceeds 0.100 T,determine the maximum current a 2.00-mm diameter niobium wire can carry and remain superconducting.(µ0 = 4π × 10−7 T⋅m/A)

Accepted Answer

A)  2000 A 
B)  1000 A 
C)  125 A 
D)  500 A

Question 20

A circular loop carrying a current of 3.0 A is oriented in a magnetic field of 0.35 T.The loop has an area of 0.24 m2 and is mounted on an axis,perpendicular to the magnetic field,which allows the loop to rotate.If the plane of the loop is oriented parallel to the field,what torque is created by the interaction of the loop current and the field?

Accepted Answer

A)  0.017 N⋅m 
B)  0.084 N⋅m 
C)  0.25 N⋅m 
D)  5.8 N⋅m

Exam 20: Induced Voltages and Inductance: Part A

Two parallel wires are separated by 0.25 m.Wire A carries 4.1 A and Wire B carries 10 A,both currents in the same direction.The magnetic permeability in empty space µ₀ = 4π × 10−⁷ T⋅m/A.The magnitude of the force on 1.4 m of Wire A is:

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:

A proton,which moves perpendicular to a magnetic field of 0.60 T in a circular path of radius 0.080 m,has what speed? (q_p = 1.6 × 10−¹⁹ C and m_p = 1.67 × 10−²⁷ kg)

A superconducting wire carries a current of 10⁴ A.Find the magnetic field at a distance of 0.25 m from the wire.(µ₀ = 4π × 10−⁷ T⋅m/A)

Which of the following devices makes use of an electromagnet?

A high-voltage power line 20 m above the ground carries a current of 5000 A.What is the magnetic field due to the current directly underneath the power line? (µ₀ = 4π × 10−⁷ T⋅m/A)

A copper wire of length 10 cm is in a magnetic field of 0.30 T.If it has a mass of 20 g,what minimum current through the wire would cause a magnetic force equal to its weight?

The magnetic domains in a magnetized piece of iron are characterized by which orientation?

A 2.0-m wire segment carrying a current of 0.60 A oriented parallel to a uniform magnetic field of 0.25 T experiences a force of what magnitude?

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?

Two long parallel wires 15 cm apart carry currents of 5.0 A and 8.0 A in the same direction.Is there any point between the two wires where the magnetic field is zero?

At the Fermilab accelerator in Weston,Illinois,singly-charged ions with momentum 3.2 × 10−¹⁶ kg⋅m/s are held in a circular orbit of radius 1 km by an upward magnetic field.What B-field must be used to maintain the ions in this orbit? (qion = 1.6 × 10−¹⁹ C)

Superconductors can carry very large currents with no resistance.If a superconducting wire is formed into a solenoid of length 50.0 cm with 250 turns,what is the magnetic field inside the solenoid when the current is 10⁴ A? (µ₀ = 4π × 10−⁷ T⋅m/A)

A proton moving with a speed of 6.0 × 10⁵ m/s perpendicular to a uniform magnetic field of 0.20 T will follow which of the paths described below? (q_p = 1.6 × 10−¹⁹ C and m_p = 1.67 × 10−²⁷ kg)