3b.3 - Magnetic Fields and The Motor Effect

Question 1

Define magnetic field

Answer 1

A region where magnetic materials and wires carrying currents experience a force acting on them

Question 2

How can magnetic fields be represented?

Answer 2

Field diagrams

Question 3

What do the field diagrams look for for a magnet?

Answer 3

A semi circle from the north pole to the south pole with arrows

Question 4

What do you need to remember when drawing field diagrams?

Answer 4

Arrows

Question 5

What way do arrows go on a magnetic field diagram?

Answer 5

North to south pole

Question 6

Describe the magnetic field around a coil of wire

Answer 6

Concentric circles with a wire in the centre

Question 7

What is a solenoid?

Answer 7

A coil of wire

Question 8

What is the magnetic field like inside a coil of wire?

Answer 8

Strong and uniform

Question 9

What is an electromagnet?

Answer 9

A magnet whose magnetic field can be turned on and off with an electric current

Question 10

What does putting a magnetically soft iron core through the middle of the wire do to it?

Answer 10

Increase the strength of the magnetic field

Question 11

What is a magnetically soft material?

Answer 11

A material that magnetises and demagnetises very easily

Question 12

Where are electromagnets useful?

Answer 12

In cranes

Question 13

What is the motor effect?

Answer 13

The force experienced by a current-carrying wire in a magnetic field

Question 14

What happens to the force if the current is made bigger?

Answer 14

It is made bigger

Question 15

What happens to the force if the magnetic field if made is made bigger?

Answer 15

It is made bigger

Question 16

How is your hand positioned in Fleming’s left hand rule? (4)

Answer 16

• Thumb up
• First finger forward
• Second finger right
• Each at 90 degrees to each other

Question 17

What does the thumb stand for in Fleming’s left hand rule?

Answer 17

Motion

Question 18

What does the first finger stand for in Fleming’s left hand rule?

Answer 18

Field

Question 19

What does the second finger stand for in Fleming’s left hand rule?

Answer 19

Current

Question 20

How do simple electric motors work? (3)

Answer 20

• Forces act in opposite directions on the two side arms in the coil of wire
• The coil is on a spindle and the opposite directions make it rotate
• The split ring commutator swaps the contacts every half turn to keep the motor turning in the same direction

Question 21

How can the direction of the motor change? (2)

Answer 21

• Swapping the polarity of the direct current supply

- Swapping the magnetic poles

Question 22

Which two factors speed up a motor? (2)

Answer 22

• More current

- Stronger magnetic field

Question 23

Where are motors used?

Answer 23

Fans, CD players etc.