Question 1

If the magnetic field   is uniform over the area bounded by a circle with a radius R, the net current through the circle is:

Accepted Answer

A)  0 
B)  2 $\pi$RB$\mu$0 
C)   $\pi$R2B/$\mu$0 
D)  RB/2$\mu$0 
E)  2RB/$\mu$0 
A)  0 
B)  2 $\pi$RB$\mu$0 
C)   $\pi$R2B/$\mu$0 
D)  RB/2$\mu$0 
E)  2RB/$\mu$0

Question 2

Two long straight wires are parallel and carry current in the same direction. The currents are 8.0 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 
A)  0 
B)  4.0* 10-4 
C)  8.0 * 10-4 
D)  12 * 10-4 
E)  20 *10-4

Question 3

A solenoid is 3.0 cm long and has a radius of 0.50 cm. It is wrapped with 500 turns of wire carrying a current of 2.0 A. The magnetic field at the center of the solenoid is:

Accepted Answer

A)  9.9 * 10-8 
B)  1.3 *10-3 
C)  4.2 * 10-2 
D)  16 T 
E)  20 T 
A)  9.9 * 10-8 
B)  1.3 *10-3 
C)  4.2 * 10-2 
D)  16 T 
E)  20 T

Question 4

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 
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 5

Two long straight current-carrying parallel wires cross the x axis and carry currents I and 3I in the same direction, as shown. At what value of x is the net magnetic field zero?

Accepted Answer

A)  0 
B)  1 
C)  3 
D)  5 
E)  7 
A)  0 
B)  1 
C)  3 
D)  5 
E)  7

Question 6

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 
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 7

A hollow cylindrical conductor (inner radius = a, outer radius = b) carries a current i uniformly spread over its cross section. Which graph below correctly gives B as a function of the distance r from the center of the cylinder?

Accepted Answer

A)  I 
B)  II 
C)  III 
D)  IV 
E)  V 
A)  I 
B)  II 
C)  III 
D)  IV 
E)  V

Exam 29: Magnetic Fields Due to Currents

If the magnetic field is uniform over the area bounded by a circle with a radius R, the net current through the circle is:

Two long straight wires are parallel and carry current in the same direction. The currents are 8.0 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:

A solenoid is 3.0 cm long and has a radius of 0.50 cm. It is wrapped with 500 turns of wire carrying a current of 2.0 A. The magnetic field at the center of the solenoid 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 long straight current-carrying parallel wires cross the x axis and carry currents I and 3I in the same direction, as shown. At what value of x is the net magnetic field zero?

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

A hollow cylindrical conductor (inner radius = a, outer radius = b) carries a current i uniformly spread over its cross section. Which graph below correctly gives B as a function of the distance r from the center of the cylinder?

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