Self-Test: Electromagnetism (Induction) Test #1
Suggested Time: 65 minutes

1. A part of a coil of wire is placed in a uniform magnetic field as shown. Which two directions of motion would immediately induce an emf in the coil? A. 1 and 2 B. 1 and 3 C. 2 and 3 D. 2 and 4

2. Four conductors of different lengths are moved through a uniform magnetic field at the same speed. Which conductor will induce the greatest emf?

 A. 1 B. 2 C. 3 D. 4

3. A step-down transformer has a 500 turn primary that operates at 120 V ac. Which of the following sets of conditions best describes the number of secondary turns and secondary voltage of this transformer? 4. What are the units of torque?
 A. N × m B. N/m C. N × s D. N/s

5. A single coil of wire of area 6.0 × 10 -3 m2 is positioned in a uniform 0.18 T magnetic field as shown. The coil is rotated 90° about axis XY in 4.2 × 10 -3 s. What average emf is induced by the coil? A. 0 V B. 0.13 V C. 0.26 V D. 43 V

6. A flexible loop of wire of area 4.5 × 10-2  m2 is positioned in a 0.17 T magnetic field as shown in Figure A. The loop is then stretched until its area is zero in a time of 0.35 s (Figure B). What is the average induced emf in the circuit and the direction of the current through resistor R? 7. A 0.20 m conductor moves at 12 m/s through the 0.60 T field shown below. Calculate the emf induced in the conductor while passing through the field. A. 0 V B. 0.13 V C. 1.4 V D. 1.8 V

8.

As an aircraft flies horizontally over the North Pole, a 0.80 V potential difference is induced across the wings. If the aircraft now slows to one half of the original speed, what will the new potential difference be?

 A. 0.40 V B. 0.57 V C. 0.80 V D. 1.6 V

9.

In a step-up transformer, how do the primary and secondary voltages, and the primary and secondary currents, compare to one another?
 A. Vs > Vp and Is > Ip B. Vs > Vp and Is < Ip C. Vs < Vp and Is > Ip D. Vs < Vp and Is < Ip

10. Two solenoids S1 and S2 are placed close together as shown in the diagram below. Immediately after the switch is closed, what is the direction of current flow through galvanometer G and what is the direction of the magnetic field produced by this current at position P inside solenoid S2? 11.

An electric motor is connected to a constant source of potential. Considering back emf, which of the following observations is correct?
 A. At full speed the applied voltage increases. B. At full speed the armature resistance increases. C. If the motor is kept from rotating at full speed, the armature heats up. D. If the motor is kept from rotating at full speed, the armature temperature decreases.

12.

Which of the following statements provides valid reasoning for the transmission of electric energy at high potential?
 A. At high potential there will be low current resulting in low power loss. B. At high potential there will be high current resulting in high power loss. C. At high potential there will be low line resistance resulting in low power loss. D. At high potential there will be high line resistance resulting in high power loss.

13. A coil of 150 turns and an area of 2.0 × 10 -4 m2 is placed in a 1.00 T magnetic field as shown in Diagram I. If this field changes to 0.45 T in 0.060 s, what is the average emf induced in the coil and in what direction does the induced current flow? 14. For what type of input current will the output current in a transformer be zero?
 A. dc B. ac C. increasing dc D. decreasing dc

15. The graph below shows how the magnetic flux through a single loop changes with respect to time. What is the average emf induced between t = 2.0 × 10 -3 s and t = 9.0 × 10 -3 s?

 A. 1.2 × 10 -4 V B. 1.8 V C. 3.6 V D. 25 V

16.

Which of the following is a statement of Lenz's law?

A. The number of magnetic lines perpendicular to the surface area enclosed by a circuit is equal to the flux.

B. An induced current in a closed conducting loop will appear in such a direction that it opposes the change that created it.

C. An emf is produced between the ends of a straight wire when the wire is moving perpendicularly through a uniform magnetic field.

D. The average emf induced in a circuit is proportional to the rate of change of the magnetic flux through that circuit.

17. A bar magnet is dropped through a solenoid, as shown.. What is the direction of the induced current in the solenoid as the magnet enters the top (i) and as the magnet leaves the bottom (ii)? 18. A solenoid of length 0.85 m has a radius of 0.10 m . A current of 25 A flows through its 7600 turns. Within this solenoid, a 0.12 m wire moves as shown and develops an emf of 0.055 V across its ends. With what speed is the wire moving perpendicular to the solenoid's magnetic field? (7marks)

19. A motor is connected to a constant 120 V source and draws a current of 38.0 A when it first starts up. At its normal operating speed, the motor draws a current of 2.50 A.

a) What is the resistance of the armature coil? (3 marks)

b) What is the back emf at normal speed? (4 marks)

c) Using principles of physics, explain why a motor draws a much higher current when jammed than when running freely. (4 marks)

20. An electric device operates on 9.0 V ac and has a total resistance of 21 W. An ideal transformer is used to change the incoming line voltage of 120 V ac to the operating voltage of 9.0 V ac.

a) Is the transformer a step-up or step-down transformer? (1 mark)

b) What is the current in the primary side? (6 marks)

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