Magnetic Effects of a Current

Question 1

when is a magnetic field created

Answer 1

when an electric current (charge) flows through a wire

Question 2

Direct current (d.c.)

Answer 2

Creates a constant magnetic field

Question 3

Alternating current (a.c.)

Answer 3

Creates an alternating magnetic field

Question 4

When the wire is arranged as a coil (known as a solenoid), the resulting magnetic field is

Answer 4

the same as that of a bar magnet

Question 5

General direction of the current flow (left to right) indicates

Answer 5

the direction of the magnetic field in the solenoid

Question 6

The areas where the field lines are closest together indicate

Answer 6

where the field is strongest;in this case, inside the solenoid

Question 7

To increase the strength of the magnetic field you can:

Answer 7

• Increase the current through the solenoid
• Increase the number of turns of wire in the solenoid

Question 8

Supplying a coil with an alternating current (a.c.) has the effect of

Answer 8

changing the direction of the current and, therefore, the direction of the magnetic field every half cycle

Question 9

Properties of electromagnets

Answer 9

• Very useful
• Can be designed to be extremely strong
• Can be turned off and on with a switch

Question 10

where are electromagnets commonly used

Answer 10

in cranes to sort scrap metal, door lock, relays and school bells

Question 11

how the electromagnet work

Answer 11

A flow of current results in the generation of a magnetic field around a coil.

The magnetic field will attract a magnetic material, for example an iron bar, and close the circuit.

The closed circuit will now perform an action, such as ringing a bell, turning on a different circuit or locking a door.

Question 12

what is a relay

Answer 12

device used to switch between separate circuits

Question 13

how does a relay work

Answer 13

• When an electromagnet is supplied with current, magnetic field is generated
• The field attracts the iron bar, which is pivoted and allows the conducting contacts at A to touch. The second circuit containing the lamp is now closed and current flows

Question 14

how does a speaker cone work

Answer 14

• A speaker cone can be seen to oscillate left and right when an alternating current is supplied to the coil
• Magnetic field due to the alternating current in the coil either attracts or repels a permanent magnet around it, resulting in the vibrations necessary for sound.