Magnetism & Electromagnetism

Question 1

What do magnets produce?

Answer 1

A magnetic field

Question 2

How many poles do magnets have?

Answer 2

2 North and South

Question 3

What is a magnetic field?

Answer 3

A region where magnetic materials (e.g. iron) experience a force

Question 4

What do magnetic field lines do?

Answer 4

Show the size and direction of the magnetic fields, They always point from NORTH –> SOUTH

Question 5

What is a magnetically soft material?

Answer 5

A material that can become an induced (or temporary) magnet when it is in a magnetic field. It stops acting like a magnet relatively quickly.

Question 6

What is a magnetically hard material?

Answer 6

A material (e.g. steel) that will remain magnetised until demagnetised. It will attract or repel other magnets.

Question 7

How can a magnet be demagnetised?

Answer 7

By disrupting the domains by heat or force (beating the magnet)

Question 8

What is a solenoid

Answer 8

A coil of wire that is part of an electric circuit. While current is flowing the coil has a magnetic field around it. The more coils there are the stronger the magnetic field.

Question 9

What is an electromagnet?

Answer 9

A solenoid with an iron core (magnetically soft), which only has a magnetic field when the current is flowing.

Question 10

What is the benefit of having an electromagnet?

Answer 10

Being able to turn the magnet on or off.

Question 11

What does an electric current in a conductor produce?

Answer 11

A magnetic field.

Question 12

When might an electromagnet be used in industry?

Answer 12

At a recycling centre to be able to lift and then drop materials - such as old cars.

Question 13

What is the right-hand grip rule?

Answer 13

Applies to magnetic fields near a straight wire The thumb points in the direction of the current and the fingers curl in the direction of the magnetic field lines.

Question 14

What happens to the magnetic field if the electric current is increased?

Answer 14

It gets STRONGER

Question 15

What shape is the magnetic field around a straight wire?

Answer 15

concentric circles around the straight wire

Question 16

What shape is the magnetic field around a flat circular coil?

Answer 16

Similar to that of a bar magnet - concentric ellipses (stretched circles) around the coil.

Question 17

What is the magnetic field like inside a current-carrying solenoid?

Answer 17

Strong and uniform

Question 18

What is the magnetic field like outside a current-carrying solenoid?

Answer 18

Like the field on a bar magnet. The ends of the solenoid act like the north and south poles on a magnet. This is called an electromagnet.

Question 19

Why is iron used in transformers?

Answer 19

Because it can magnetise and demagnetise quickly mains electricity needs to do this 50 times a second = 50Hz

Question 20

When can the motor effect happen?

Answer 20

When a current carrying wire is put in a magnetic field.

Question 21

What happens when a current-carrying wire is put between magnetic poles?

Answer 21

The 2 magnetic fields affect one another causing a force on the wire. This causes the wire to move. this is called the motor effect

Question 22

At what angle to the magnetic field does the wire have to be to feel the full force?

Answer 22

90 degrees

Question 23

What happens if the wire runs along the magnetic field?

Answer 23

No force is felt

Question 24

What happens to the strength (magnitude) of the force when the magnetic field increases?

Answer 24

It increases

Question 25

What happens to the strength (magnitude) of the force when the current increases?

Answer 25

It increases

Question 26

What happens if the current or magnetic field is reversed?

Answer 26

The direction of the force is also reversed.

Question 27

Which rule tells you which way a force acts in the motor effect?

Answer 27

Flemmings left-hand rule. thuMb = Motion First Finger = Field seCond finger = Current

Question 28

What 4 factors speed up a simple DC electric motor?

Answer 28

1. more current 2. more turns on the coil 3. stronger magnetic field 4. soft iron core in the coil

Question 29

Explain how a simple DC motor works

Answer 29

1. Forces act on the 2 side arms of the coil - 1 up and 1 down 2. the coil is on a spindle so it rotates 3. The split ring commutator swaps the contact every half turn to keep the motor rotating in the same direction 4. The sirection of the motor is reversed by swapping the polarity of the d.c. supply or by swapping the poles over 5. The speed is increased by adding more turns to the coil, or by increasing the current or by increasing the strength of the magnetic field ir by adding a soft iron core 6. You can use Flemmings left hand rule to work out which way the coil will turn

Question 30

How do loud speakers work?

Answer 30

using the motor effect 1. AC electrical sugnals from an amplifier are fed to a coil of wire in the speaker 2. The coil is surrounded by a permanent magnet -\> the a.c. signals cause a force on the coil and make it move back and forth 3. These movements make the cone vibrate and this creates sounds.

Question 31

What is EM or electromagnetic induction?

Answer 31

The creation of voltage in a wire which is experiencing a change in magnetic field