Problem Set 2.13: Electromagnetism Instructions: Read your textbook from page 72 to 85. Answer the questions that follow. Keep this assignment in your portfolio.

1. Use the right-hand rule to predict the direction of a compass needle in each of the examples shown in Figure 4.25 on page 79 (sketch each picture and determine the magnetic field direction).

a) b) c)

counterclockwise coming out at the top going to right

(see top of page 75) going in on the bottom

use the right hand rule!

2. Use the right-handed rule to predict the positive terminal of the battery in each of the examples shown in Figure 4.26 on page 80.

a) b)

current is going into page current is counterclockwise

use the right hand rule!

3. Figure 4.27 on page 80 shows an electromagnet made by wrapping a few turns of wire around a steel nail. Apply the right-hand rule to one turn and figure out which end of the electromagnet, A or B, is the North Pole.

Grab the wire (imagine that you can). Your thumb is placed in the direction of the current.

Your fingers would point upwards indicating that B is the South Pole (fingers are pointing

like a compass needle with the ends of your fingers being like the north – and remember north

points to south!) . This means that A is the North!

4. Suggest two ways in which you could strengthen the electromagnet in Figure 4.27 on page 80.

1. increase the current

2. have more turns of wire

5. Sketch Figure 4.27 on page 80 in your notebook and draw a few lines of force around, showing what its magnetic field would look like.

It looks like a permanent bar magnet with the area at B being a South Pole (and A being North)

6. List three ways in which the amount of electricity from an electric generator can be increased.

Use a coil made with many more wraps of wire

Move the magnet through a coil of wire faster

Use a stronger magnet

7. a) What is the meaning of DC?

Direct current – current that flows in only one direction

b) List three devices that use DC.

television

stereo

simple circuits that use batteries

8. a) What is the meaning of AC?

Alternate current – current that flows in back and forth (usually very quickly changing e.g. 60 times per second)

b) Name two sources of AC.

BC Hydro Power Company

Simple generator

9. Electricity is supplied to the armature of a generator through brushes and rings. Explain why continuous wires cannot be used for this purpose.

The wire would get tied up into a knot quickly. In this way there is a continuous current flow.

10. All large generators like those used by B.C. Hydro, use electromagnets, whereas bicycle generators use permanent magnets. State a reason for this difference.

The generator used in a bicycle light is simple and cheap. It requires no additional current flow through the armature to help control the magnetic field. The B.C. hydro generators are more complex and costly (but more efficient).

11. If you had a generator supplying electricity to some appliances connected in parallel, would you expect any change in the generator as more appliances are turned on?

There is more current drawn with more devices in parallel connected. The generator may be required to produce more electricity to satisfy the needs of the devices. However, the amount of electricity generated is related to how fast the magnets and wires are changed relative to each other.