Magnetism And Electromagnetism

Question 1

What is a magnetic field?

Answer 1

-region where magnets and magnetic materials experience a force (non contact)

Question 2

What poles do magnets have?

Answer 2

-North and South

Question 3

How could you show a magnetic field?

Answer 3

• place a bar magnet under a piece of paper
• shake iron fillings onto top of paper
• will see the force lines of the magnet and where the strongest magnetic field is
• strongest magnetic field is at the poles of the magnet (lines are closer together)

Question 4

What happens when a North magnet is placed near a South magnet?

Answer 4

• exert a force on each other (attractive or repulsive)
• two unlike poles will attract each other strongly
• two like poles will repel each other

Question 5

What is the magnetic North Pole on a compass?

Answer 5

The geographic South Pole (opposites)

Question 6

What does a current carrying conductor have?

Answer 6

• circular magnetic field around it
• direction of field depends on direction or current
• if current coming towards you, the circular field is anti clockwise

Question 7

Where is the magnetic field in a coiled wire (solenoid)?

Answer 7

• goes through centre of coil

- if magnetic field in a clockwise direction, the magnetic field direction through coil is away from you

Question 8

What is the right hand thumb rule?

Answer 8

using right hand, point thumb in direction of current and curl your fingers. The direction of fingers is the direction of the field

Question 9

What is a permanent magnet?

Answer 9

• They are magnetic all the time
• used as fridge magnets to hold things
• produce their own magnetic field

Question 10

What is an electromagnet?

Answer 10

• a magnet where the electrical current can be switched on and off (isn’t permanent)
• used in scrapyards when metal is being dropped

Question 11

How do you make an electromagnet?

Answer 11

• wrap wire around an iron nail into a coil (solenoid) and connect it to a power supply
• the current allows the nail to become magnetic when power supply is switched on
• produced a magnetic field in iron core

Question 12

How can you increase the strength of an electromagnet?

Answer 12

• increasing the number of coils it has (the closer the field lines, the stronger the field)
• increasing the current
• place a block of iron in the centre of the coil and iron core becomes an induced magnet when the current is flowing

Question 13

What happens in the circuit of an electric bell?

Answer 13

• electromagnet attracts arm of the striker towards the bell
• as striker moves towards bell, circuit contact is broken and striker springs back
• contact is remade and striker is attracted again and hits the bell and breaks circuit again

Question 14

What is an induced magnet?

Answer 14

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

Question 15

What happens when you take away the magnetic field?

Answer 15

Induced magnet quickly loses most or all of their magnetism (eg in scrap yards)

Question 16

How is an electromagnet used in a relay switch?

Answer 16

• used to enable a circuit with small current (eg light sensor) to switch on a circuit with a larger current (eg street lamp)
• when small circuit is switched on, activated electromagnet which pulls contacts of switch in the large circuit together (switching it on)

Question 17

What material is needed to create an electromagnet?

Answer 17

• easily magnetised and demagnetised
• soft iron is the best as it doesn’t have many impurities
• steel not as good as it retains some magnetism when current is turned off

Question 18

What does the direction of magnetic field depend on?

Answer 18

The direction of the current

Question 19

How could you investigate the magnetic field between four bar magnets?

Answer 19

• put magnets on a piece of paper and place many compasses in different places between magnets to show magnetic field at those points
• compass needles will line up with magnetic field lines

Question 20

What is the motor effect?

Answer 20

When a current carrying wire is put between magnetic poles, the magnetic field around the pole interacts with the magnetic field it has been placed in

• this causes magnet and the conductor to exert a force on each other
• motor effect can cause wire to move

Question 21

What is Flemming’s left hand rule?

Answer 21

Using left hand, point first finger in direction of field

Point second finger in direction of current

Your thumb will then point in direction of the force (motion)

Question 22

How do you find the size of a force acting on a conductor in a magnetic field?

Answer 22

Force =magnetic flux density (Tesla) X current X length

Question 23

What is the generator effect?

Answer 23

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

Question 24

What is a generator?

Answer 24

Rotated a coil in a magnetic field or a magnet in a coil

Question 25

What is a dynamo?

Answer 25

They have a slip ring commutator instead of slip rings which swaps connection every half turn to keep current flowing in same direction

Question 26

What does a transformer do?

Answer 26

Uses the generator effect to change size of a pd. They will only work with alternating current

Question 27

What do transformers always have?

Answer 27

Two coils of wire, the primary and secondary, joined with an iron core

Question 28

What is the transformer equation?

Answer 28

Input pD/output pD = no of turns in primary coil / no of turns in secondary coil

Question 29

What does a step up transformer do?

Answer 29

Step the pd up. Have more turns on secondary coil then primary coil

Question 30

What does a step down transformer do?

Answer 30

Step the pd down. Have more turns on primary coil than secondary