Magnetism and electromagnetism

Question 1

What is a permanent magnet?

Answer 1

A magnet that produces it’s own magnetic field

Question 2

What is an induced magnet?

Answer 2

Magnetic materials that turn into a magnet when they’re put into a magnetic field

Question 3

How does a compass work?

Answer 3

Inside is a bar magnet; the north pole is attracted to the south pole of any magnet near which means that it points in the direction of any magnetic field, including the earth’s own one, which is why a compass always points north

Question 4

What happens when a current flows through a wire?

Answer 4

A magnetic field is produced around the wire, made up of concentric circles perpendicular to the wire

Question 5

How can the strength of a magnetic field be effected?

Answer 5

The larger the current is or the closer to the wire you are, the stronger the magnetic field

Question 6

What is a solenoid?

Answer 6

A coil of wire

Question 7

How can a solenoid be used for a magnetic field?

Answer 7

By wrapping the wire into a solenoid, the strength of the magnetic field is increased as the field lines around each loop of wire line up with each other, meaning that there are lots of field lines pointing in one direction

Question 8

How can you increase the field strength of a solenoid?

Answer 8

By putting a block of iron in the centre as it turns into an induced magnet (this is called an electromagnet) or by adding more coils to it

Question 9

Why are electromagnets useful?

Answer 9

They only work when a current is flowing through the solenoid, meaning they can be turned on and off, which a permanent magnet can’t

Question 10

What are the main uses of electromagnets?

Answer 10

In scrap yards to pick up then release certain metals and within other circuits to act as switches

Question 11

What is the motor effect?

Answer 11

When a current carrying wire is put between magnetic poles, the magnetic field around the wire interacts with the magnetic field it has been placed in. This causes the magnet and the conductor to exert a force on each other

Question 12

How can the wire experience the full force during the motor effect?

Answer 12

The wire has be at 90 degrees to the magnetic field as the force always acts at right angles to the magnetic field and the direction of the current in the wire

Question 13

How does the force acting on the wire become increased?

Answer 13

If the strength of the magnetic field is increased or if the current running through the wire is increased

Question 14

How do you find the size of the force acting on a wire?

Answer 14

Magnetic flux density x current x length

Question 15

Which fingers represent what in Fleming’s left hand rule?

Answer 15

The thumb is force, the first finger is field and the second finger is current

Question 16

How can the direction of the motor by reversed in a magnetic field?

Answer 16

By reversing the current or by swapping the magnets

Question 17

How does a loudspeaker work?

Answer 17

An ac is sent through a coil of wire which surrounds one magnetic pole and is surrounded by the other and is attached to the base of a paper cone, the force acts in the opposite direction when the current reverses, variations in the current cause the cone to vibrate, causing the air particles to vibrate and variations in pressure create a sound wave

Question 18

What is the generator effect?

Answer 18

The induction of a potential difference (and current if there’s a complete circuit) in a wire which is moving relative to a magnetic field, or experiencing a change in magnetic field

Question 19

How do you create current in the generator effect?

Answer 19

By moving a magnet in a coil of wire from side to side, a small amount of current will be created but only whilst the magnet is still moving

Question 20

How is alternating current produced in the generator effect?

Answer 20

Moving the magnet or conductor in the opposite direction will reverse the potential difference/current, so if you keep the magnet moving backwards and forwards, a potential difference is produced which keeps swapping direction

Question 21

What happens when a change in the magnetic field induces a current in the wire?

Answer 21

When a current flows ANOTHER magnetic filed is induced around the wire

Question 22

What does a magnetic field created by an induced current do?

Answer 22

It always acts against the change that made it

Question 23

How do you change the size of an induced pd?

Answer 23

You have to change the rate that the magnetic field is changing

Question 24

How do you increase induced pd?

Answer 24

Increase the speed of the movement or increase the strength of the magnetic field

Question 25

How do alternators generate alternating current?

Answer 25

They work just like generator, except instead of a split ring commutator, they have slip rings and brushes so that the contacts don’t swap every half turn to keep it the same direction; this means they produce an alternating potential difference

Question 26

How does a dynamo generate direct current?

Answer 26

It works in the same way as alternators except has a split-ring commutator instead of slip rings which swaps the connection every half turn to keep the current flowing int the same direction

Question 27

How does a microphone work?

Answer 27

Sound waves hit a flexible diaphragm that is attached to a coil of wire wrapped around a magnet, causing the coil of wire to move in the magnetic field, generating a current. This sis basically the opposite of a loudspeaker