Magnetism And Electromagnetism Flashcards Preview

Physics Paper 2 > Magnetism And Electromagnetism > Flashcards

Flashcards in Magnetism And Electromagnetism Deck (30)
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1
Q

What is a magnetic field?

A

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

2
Q

What poles do magnets have?

A

-North and South

3
Q

How could you show a magnetic field?

A
  • 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)
4
Q

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

A
  • exert a force on each other (attractive or repulsive)
  • two unlike poles will attract each other strongly
  • two like poles will repel each other
5
Q

What is the magnetic North Pole on a compass?

A

The geographic South Pole (opposites)

6
Q

What does a current carrying conductor have?

A
  • circular magnetic field around it
  • direction of field depends on direction or current
  • if current coming towards you, the circular field is anti clockwise
7
Q

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

A
  • goes through centre of coil

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

8
Q

What is the right hand thumb rule?

A

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

9
Q

What is a permanent magnet?

A
  • They are magnetic all the time
  • used as fridge magnets to hold things
  • produce their own magnetic field
10
Q

What is an electromagnet?

A
  • a magnet where the electrical current can be switched on and off (isn’t permanent)
  • used in scrapyards when metal is being dropped
11
Q

How do you make an electromagnet?

A
  • 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
12
Q

How can you increase the strength of an electromagnet?

A
  • 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
13
Q

What happens in the circuit of an electric bell?

A
  • 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
14
Q

What is an induced magnet?

A

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

15
Q

What happens when you take away the magnetic field?

A

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

16
Q

How is an electromagnet used in a relay switch?

A
  • 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)
17
Q

What material is needed to create an electromagnet?

A
  • 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
18
Q

What does the direction of magnetic field depend on?

A

The direction of the current

19
Q

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

A
  • 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
20
Q

What is the motor effect?

A

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
21
Q

What is Flemming’s left hand rule?

A

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)

22
Q

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

A

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

23
Q

What is the generator effect?

A

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

24
Q

What is a generator?

A

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

25
Q

What is a dynamo?

A

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

26
Q

What does a transformer do?

A

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

27
Q

What do transformers always have?

A

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

28
Q

What is the transformer equation?

A

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

29
Q

What does a step up transformer do?

A

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

30
Q

What does a step down transformer do?

A

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