P3.2 (The motor effect)

Question 1

Fill in the blank: A ____ field is created when an electric current flows through a wire.

Answer 1

Magnetic

Question 2

Why do electromagnets have a strong magnetic field?

Answer 2

Electromagnets have strong magnetic fields due to the coiling of wire around a soft iron core.

Question 3

What is a current?

Answer 3

Moving electric charges

Question 4

The magnetic field is only present when the current is flowing, true or false?

Answer 4

True

Question 5

How does an electromagnet work?

Answer 5

Wire is wrapped around a soft iron core, and an electric current passed through it. The electromagnet behaves as if it were a bar magnet, except that it can be switched on and off.

Question 6

Give four examples of magnetic materials

Answer 6

Iron, steel, nickel and colbalt

Question 7

Give some uses for electromagnets

Answer 7

Electromagnets are used on cranes to lift and drop iron and steel in scrapyards, recycling centres and steel works.

Question 8

How does an electric bell work?

Answer 8

1. When the current flows through the circuit, the electromagnet makes a magnetic field.
2. The electromagnet attracts the springy metal arm.
3. The arm hits the gong, which makes a sound.
4. The circuit is broken now the arm is out of position.
5. The electromagnet is turned off and the springy metal arm moves back.
6. The circuit is complete again.
   The cycle repeats as long as the switch is closed.

Question 9

Fill in the blanks: A simple electric motor can be built using a coil of wire that is free to ___ between two opposite _____ _____.

Answer 9

Rotate

Magnetic Poles

Question 10

What is the ‘motor effect’?

Answer 10

A simple electric motor can be built using a coil of wire that is free to rotate between two opposite magnetic poles.

Question 11

In the motor effect, what wire positioning makes the force greatest?

Answer 11

This size of the force is greatest when the wire is perpendicular to the magnetic field of the permanent magnet. In other words, it cuts through the magnetic field at 90°. If the wire is parallel to the magnetic field, it will not experience any force.

Question 12

How do you conduct the ‘Flemings left-hand rule’?

Answer 12

1. Spread out your left thumb, forefinger (index finger) and second finger so they are all at 90° to one another:
2. Point your forefinger (index finger) in the direction of the magnetic field (north to south)
3. Point your second finger in the direction of the electric current (positive to negative)
   Your thumb will point in the direction of movement.

Question 13

The direction of the current must be _____ every half turn, otherwise the coil comes to a halt again. This is achieved using a conducting ring split in two, called a split ring or ‘_____’.

Answer 13

Reversed

Commutator

Question 14

How would you increase the size of the force on a wire carrying a current?

Answer 14

Increase the size of the current.

Increase the size of the magnetic field