Self-Test: Electromagnetism (Induction) Test #2
Suggested Time: 65 minutes
 
1.

Transformers are commonly used in which electrical device?

A. toaster

B. television set

C. electric kettle

D. incandescent bulb

 
2.

A solid conductor travels at 150 m/s across a uniform 0.045 T magnetic field. Which side is positively charged and what is the emf across this block?

3. A long conductor is placed in a 0.65 T magnetic field as shown below.

What are the magnitude and direction of the current that produces a 1.6 N force on the wire directed up the page?

 

4.

A motor operating at full speed draws a current of 4.0 A when connected to a 110 V source. The motor has an armature resistance of 3.5 W . What is the back emf at full speed?

A. 14 V

B. 96 V

C. 110 V

D. 124 V

 
5.

An ideal transformer with 120 Vac on the primary coil supplies power to the resistor R. If this resistor dissipates 35 W, what is the current in the primary coil and in the secondary coil?

 
6.

A 500-turn circular coil with an area of 1.54 ×10-2  m2 is perpendicular to a 0.060 T field. The  magnetic field changes to 0.020 T in the opposite direction in 0.12 s.

What is the average emf induced in the coil?

A. 5.1 ×103 V

B. 1.0 ×102 V

C. 2.6 V

D. 5.1 V

7. A metal block moves with a constant speed in a uniform magnetic field.

Which side of the block is positive?

A. JK

B. KL

C. LM

D. MJ

 
8.

A 0.75 m conducting rod is moved at 8.0 m/s across a 0.25 T magnetic field along metal rails. The electrical resistance of the system is 5.0 W.

What are the magnitude and direction of the current through point X?

 

9. A bar magnet is moving toward a solenoid.

What is the direction of the current through the galvanometer and what is the direction of the magnetic field produced by this current at location P inside the solenoid?

 
10.

The 5.2 m long metal rotor blades of a helicopter spin at 6.0 revolutions per second perpendicular to the earth’s magnetic field of 4.7 ´10-5 T.

What is the magnetic flux swept out by the rotor blades in one revolution and what is the emf induced between the axis and tip of a rotor blade?

 

11.

An electric motor rotates at various speeds and the current through the armature changes accordingly. Which pair of conditions occurs when the motor generates the greatest back emf?

 

12.

A transformer connected to a 120 V ac supply has 7 000 primary and 350 secondary windings. It delivers a secondary current of 2.4 A. Find the primary current and secondary voltage.

 
13. The diagram below shows two coils in a magnetic field.

An electric current can be induced in the coil oriented with its plane

A. parallel to a constant magnetic field.

B. parallel to a changing magnetic field.

C. perpendicular to a constant magnetic field.

D. perpendicular to a changing magnetic field.

 

14.

The diagram shows a 0.010 kg metal rod resting on two long horizontal frictionless rails which remain 0. 40 m apart. The circuit has a resistance of 3.0 W and is located in a uniform 0.20 T magnetic field.

Find the initial acceleration and maximum velocity for the rod.

 

15.

The diagram shows a bar magnet falling through an aluminum pipe. Electric currents are induced in the pipe immediately above and below the falling magnet. In which direction do these currents flow?

 
16.

The diagram below shows an aluminum ring and the current induced in it by the nearby magnet that is free to move along its central axis.

The magnet must be

A. stationary.

B. moving to the left.

C. moving to the right.

D. spinning about its central axis.

 

17.

A computer adapter contains a transformer that converts 120 V ac across its primary windings to 24 V ac across its secondary windings. The primary current is 1.2 A. What is the secondary current and what is the type of transformer?

 

18.

A loop of wire of area 0.32 m2 is placed in a 0.75 T magnetic field as shown. The magnetic field is changed to 0.35 T in the opposite direction in 0.45 s.

What are the magnitude and direction of the current through the 15 W resistor?

 

19.

The diagram shows a coil with 25 windings and dimensions 0.15 m by 0.20 m. Its plane is perpendicular to a magnetic field of magnitude 0.60 T.

If the coil rotates 90° in 4.17 ´10-2 s so that its plane is now parallel to the magnetic field, what average emf is induced during this time? (7 marks)

 

20.

An electric motor is connected to a 9.0 V power supply. The data table below shows how the back emf of the motor, Vback , varies with the current through the armature, I , as the mechanical load changes.

a) Plot this data on the graph below. (2 marks)

b) Determine the slope of this graph. (2 marks)

c) What property of the motor does the slope of this graph represent? (1 mark)

 

 
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