Secondary 3 October Exam

1) A wire carries a current, creating a magnetic field around itself as shown. The current in the wire is:

• A. Directed to the right

• A. Directed to the left

• A. Equal to the magnetic field

• In the same direction as the magnetic field

1) A solenoid with 500 turns, 0.10 m long, carrying a current of 4.0 A and with a radius of 10^2 m will have what strength magnetic field at its center?

• 31 x 10 ^{– 4} T

• 62 x 10 ^{– 4} T

• 125 x 10 ^{– 4} T

• 250 x 10 ^{– 4} T

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?

• #1

• #2

• Both have the same magnetic field.

• Since it depends on the values of A and L, none of the above are correct

1) A straight wire carries a current inside the paper. What is the direction of the magnetic field at point P?

• Points to the right

• Points to the left

• Points to the top of the page

• Points to the bottom of the page

Two parallel wires of length 2 m are separated by 40 cm. If the magnetic force between the two wires is 2 ×10^-6 N and the current in the second wire is twice the current in the first one.

1) Which of the following is true concerning the force between the two wires:

• The magnetic force is a repulsion between wires

• The magnetic force is an attraction between the wires

A circular coil of radius 5 cm and 50 turns carries a current of 3 ampere. The magnetic dipole moment of the coil is

• (a) 1.0 amp – m2

• (b) 1.2 amp – m2

• (c) 0.5 amp – m2

• (d) 0.8 amp – m2

When the plane of the loop is parallel to the magnetic field the torque on the current loop is ______________

• zero

• maximum

• minimum

• equal

1) What is the magnitude of the magnetic force per unit length between a pair of parallel wires separated by 2 m if they carry each a current of 3 A?

A.

• 1.8 x 10^–6 N/m

• 9 x 10^–7 N/m

• 4.5 x 10^–7 N/m

• 3 x 10^{– 7} N/m

A current loop is oriented in three different positions relative to a uniform magnetic field. In position 1 the plane of the loop is perpendicular to the field lines. In position 2 and 3 the plane of the loop is parallel to the field as shown. The torque on the loop is maximum in

• position 1

  
  

• position 2

• position 3

  
  

• positions 2 and 3

Concave magnetic poles, with a fixed soft-iron cylinder in a moving coil galvanometer, make the magnetic field

• Weak

• Radial

• Zero

• Infinite