Question 1

Solenoid 2 has twice the radius and six times the number of turns per unit length as solenoid 1. The ratio of the magnetic field in the interior of 2 to that in the interior of 1 is:

Accepted Answer

A)  2 
B)  4 
C)  6 
D)  1 
E)  1/3

Question 2

Two long straight wires are parallel and carry current in opposite directions. The currents are 8.0 A and 12 A and the wires are separated by 0.40 cm. The magnetic field in tesla at a point midway between the wires is:

Accepted Answer

A)  0 
B)  4.0 * 10-4 
C)  8.0 * 10-4 
D)  12 * 10-4 
E)  20 * 10-4

Question 3

Two parallel long wires carry the same current and repel each other with a force F per unit length. If both these currents are doubled and the wire separation tripled, the force per unit length becomes:

Accepted Answer

A)  2F/9 
B)  4F/9 
C)  2F/3 
D)  4F/3 
E)  6F

Question 4

In an overhead straight wire, the current is north. The magnetic field due to this current, at our point of observation, is:

Accepted Answer

A)  east 
B)  up 
C)  north 
D)  down 
E)  west

Question 5

A long straight cylindrical shell has an inner radius Ri and an outer radius Ro. It carries a current i, uniformly distributed over its cross section. A wire is parallel to the cylinder axis, in the hollow region (r i). The magnetic field is zero everywhere outside the shell (r > Ro). We conclude that the wire:

Accepted Answer

A)  is on the cylinder axis and carries current i in the same direction as the current in the shell 
B)  may be anywhere in the hollow region but must be carrying current i in the direction opposite to that of the current in the shell 
C)  may be anywhere in the hollow region but must be carrying current i in the same direction as the current in the shell 
D)  is on the cylinder axis and carries current i in the direction opposite to that of the current in the shell 
E)  does not carry any current

Question 6

In the figure, the current element  the point P, and the three vectors (1, 2, 3) are all in the plane of the page. The direction of  due to this current element, at the point P is:

Accepted Answer

A)  in the direction marked "1" 
B)  in the direction marked "2" 
C)  in the direction marked "3" 
D)  out of the page 
E)  into the page

Question 7

In Ampere's law,  the integration must be over any:

Accepted Answer

A)  surface 
B)  closed surface 
C)  path 
D)  closed path 
E)  closed path that surrounds all the current producing

Question 8

Suitable units for $\mu$0 are:

Accepted Answer

A)  tesla 
B)  newton/ampere2 
C)  weber/meter 
D)  kilogram.ampere/meter 
E)  tesla.meter/ampere

Question 9

A "coulomb" is:

Accepted Answer

A)  one ampere per second 
B)  the quantity of charge which will exert a force of 1 N on a similar charge at a distance of 1 m 
C)  the amount of current in each of two long parallel wires separated by 1 m, which produces a force of 2 * 10-7 N per meter 
D)  the amount of charge which flows past a point in one second when the current is 1 A 
E)  an abbreviation for a certain combination of kilogram, meter and second

Question 10

If the radius of a pair of Helmholtz coils is R then the distance between the coils is:

Accepted Answer

A)  R/4 
B)  R/2 
C)  R 
D)  2R 
E)  4R

Question 11

A square loop of current-carrying wire with edge length a is in the xy plane, the origin being at its center. Along which of the following lines can a charge move without experiencing a magnetic force?

Accepted Answer

A)  x = 0, y = a/2 
B)  x = a/2, y = a/2 
C)  x = a/2, y = 0 
D)  x = 0, y = 0 
E)  x = 0, z = 0

Question 12

The magnetic field at any point is given by  where  is the position vector of the point and A is a constant. The net current through a circle of radius R, in the xy plane and centered at the origin is given by:

Accepted Answer

A)   $\pi$AR2/$\mu$0 
B)  2 $\pi$AR/$\mu$0 
C)  4 $\pi$AR3/3$\mu$0 
D)  2 $\pi$AR2/$\mu$0 
E)  $\pi$AR2/2$\mu$0

Question 13

Two parallel wires, 4 cm apart, carry currents of 2 A and 4 A respectively, in opposite directions. The force per unit length in N/m of one wire on the other is:

Accepted Answer

A)  1 *10-3, repulsive 
B)  1 *10-3, attractive 
C)  4 * 10-5, repulsive 
D)  4 *10-5, attractive 
E)  none of these

Question 14

Two long parallel straight wires carry equal currents in opposite directions. At a point midway between the wires, the magnetic field they produce is:

Accepted Answer

A)  zero 
B)  non-zero and along a line connecting the wires 
C)  non-zero and parallel to the wires 
D)  non-zero and perpendicular to the plane of the two wires 
E)  none of the above

Question 15

A toroid has a square cross section with the length of an edge equal to the radius of the inner surface. The ratio of the magnitude of the magnetic field at the inner surface to the magnitude of the field at the outer surface is:

Accepted Answer

A)  1/4 
B)  1/2 
C)  1 
D)  2 
E)  4

Question 16

A constant current is sent through a helical coil. The coil:

Accepted Answer

A)  tends to get shorter 
B)  tends to get longer 
C)  tends to rotate about its axis 
D)  produces zero magnetic field at its center 
E)  none of the above

Question 17

Two long ideal solenoids (with radii 20 mm and 30 mm respectively) carry the have the same number of turnes of wire per unit length. The smaller solenoid is mounted inside the larger, along a common axis. It is observed that there is zero magnetic field within the inner solenoid is zero. The current in the inner solenoid must be:

Accepted Answer

A)  two-thirds the current in the outer solenoid 
B)  one-third the current in the outer solenoid 
C)  twice the current in the outer solenoid 
D)  half the current in the outer solenoid 
E)  the same as the current in the outer solenoid

Question 18

A long straight cylindrical shell has an inner radius Ri and an outer radius Ro. It carries a current i, uniformly distributed over its cross section. A wire is parallel to the cylinder axis, in the hollow region (r i). The magnetic field is zero everywhere in the hollow region. We conclude that the wire:

Accepted Answer

A)  is on the cylinder axis and carries current i in the same direction as the current in the shell 
B)  may be anywhere in the hollow region but must be carrying current i in the direction opposite to that of the current in the shell 
C)  may be anywhere in the hollow region but must be carrying current i in the same direction as the current in the shell 
D)  is on the cylinder axis and carries current i in the direction opposite to that of the current in the shell 
E)  does not carry any current

Question 19

The diagrams show three circuits consisting of concentric circular arcs (either half or quarter circles of radii r, 2r, and 3r) and radial lengths. The circuits carry the same current. Rank them according to the magnitudes of the magnetic fields they produce at C, least to greatest.

Accepted Answer

A)  1, 2, 3 
B)  3, 2, 1 
C)  1, 3, 2 
D)  2, 3, 1 
E)  2, 1, 3

Question 20

Helmholtz coils are commonly used in the laboratory because the magnetic field between them:

Accepted Answer

A)  can be varied more easily than the fields of other current arrangements 
B)  is especially strong 
C)  nearly cancels the Earth's magnetic field 
D)  is parallel to the plane of the coils 
E)  is nearly uniform

Exam 29: Magnetic Fields Due to Currents

Solenoid 2 has twice the radius and six times the number of turns per unit length as solenoid 1. The ratio of the magnetic field in the interior of 2 to that in the interior of 1 is:

Two long straight wires are parallel and carry current in opposite directions. The currents are 8.0 A and 12 A and the wires are separated by 0.40 cm. The magnetic field in tesla at a point midway between the wires is:

Two parallel long wires carry the same current and repel each other with a force F per unit length. If both these currents are doubled and the wire separation tripled, the force per unit length becomes:

In an overhead straight wire, the current is north. The magnetic field due to this current, at our point of observation, is:

In the figure, the current element the point P, and the three vectors (1, 2, 3) are all in the plane of the page. The direction of due to this current element, at the point P is:

In Ampere's law, the integration must be over any:

Suitable units for $\mu$ ₀ are:

A "coulomb" is:

If the radius of a pair of Helmholtz coils is R then the distance between the coils is:

A square loop of current-carrying wire with edge length a is in the xy plane, the origin being at its center. Along which of the following lines can a charge move without experiencing a magnetic force?

Two parallel wires, 4 cm apart, carry currents of 2 A and 4 A respectively, in opposite directions. The force per unit length in N/m of one wire on the other is:

Two long parallel straight wires carry equal currents in opposite directions. At a point midway between the wires, the magnetic field they produce is:

A toroid has a square cross section with the length of an edge equal to the radius of the inner surface. The ratio of the magnitude of the magnetic field at the inner surface to the magnitude of the field at the outer surface is:

A constant current is sent through a helical coil. The coil:

The diagrams show three circuits consisting of concentric circular arcs (either half or quarter circles of radii r, 2r, and 3r) and radial lengths. The circuits carry the same current. Rank them according to the magnitudes of the magnetic fields they produce at C, least to greatest.

Helmholtz coils are commonly used in the laboratory because the magnetic field between them:

Exam 29: Magnetic Fields Due to Currents

Solenoid 2 has twice the radius and six times the number of turns per unit length as solenoid 1. The ratio of the magnetic field in the interior of 2 to that in the interior of 1 is:

Two long straight wires are parallel and carry current in opposite directions. The currents are 8.0 A and 12 A and the wires are separated by 0.40 cm. The magnetic field in tesla at a point midway between the wires is:

Two parallel long wires carry the same current and repel each other with a force F per unit length. If both these currents are doubled and the wire separation tripled, the force per unit length becomes:

In an overhead straight wire, the current is north. The magnetic field due to this current, at our point of observation, is:

In the figure, the current element the point P, and the three vectors (1, 2, 3) are all in the plane of the page. The direction of due to this current element, at the point P is:

In Ampere's law, the integration must be over any:

Suitable units for μ\muμ 0 are:

A "coulomb" is:

If the radius of a pair of Helmholtz coils is R then the distance between the coils is:

A square loop of current-carrying wire with edge length a is in the xy plane, the origin being at its center. Along which of the following lines can a charge move without experiencing a magnetic force?

The magnetic field at any point is given by where is the position vector of the point and A is a constant. The net current through a circle of radius R, in the xy plane and centered at the origin is given by:

Two parallel wires, 4 cm apart, carry currents of 2 A and 4 A respectively, in opposite directions. The force per unit length in N/m of one wire on the other is:

Two long parallel straight wires carry equal currents in opposite directions. At a point midway between the wires, the magnetic field they produce is:

A toroid has a square cross section with the length of an edge equal to the radius of the inner surface. The ratio of the magnitude of the magnetic field at the inner surface to the magnitude of the field at the outer surface is:

A constant current is sent through a helical coil. The coil:

The diagrams show three circuits consisting of concentric circular arcs (either half or quarter circles of radii r, 2r, and 3r) and radial lengths. The circuits carry the same current. Rank them according to the magnitudes of the magnetic fields they produce at C, least to greatest.

Helmholtz coils are commonly used in the laboratory because the magnetic field between them:

Suitable units for $\mu$ ₀ are: