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Physics - Y10 + Y11 > Magnetism and Electromagnetism - Y11 > Flashcards

Magnetism and Electromagnetism - Y11 Flashcards

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1
Q

What do all magnets have?

A

A north pole and south pole

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2
Q

Where are the magnetic forces strongest?

A

At the poles of a magnet

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3
Q

What happens when you bring 2 magnets close together? Explain more

A

They exert a force on each other
2 like poles = repel
2 opposite poles = attract
Both non-contact forces

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4
Q

Whats a permanent magnet?

A

Produces its own magnetic field eg bar magnet

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5
Q

What happens when you bring a permanent magnet close to another permanent magnet?

A

Attract or repel each other, depending on the direction

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6
Q

What is an induced magnet?

A

Object that becomes a magnet when it is placed in a magnetic field

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7
Q

What is the force between permanent and induced magnets?

A

Always attractive

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8
Q

What happens when you take away the magnetic field from induced magnets?

A

Quickly lose their magnetism or most of it and stop producing a magnetic field

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9
Q

Whats a magnetic field?

A

Region where other magnets or magnetic materials experience a force

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10
Q

4 types of magnetic material, what can they be made into

A

Iron
Steel
Cobalt
Nickel
They can be made in a permanent or induced magnet

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11
Q

How can you find the direction of a magnetic field?

A

Compass, it points in the direction of the magnetic field its in

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12
Q

Why do compasses always point north?

A

Earth generates its own magnetic field. which shows the inside (core) of the Earth must be magnetic

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13
Q

What is inside every compass?

A

A tiny bar magnet.

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14
Q

What direction do the lines go on magnetic field lines?

A

North to south

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15
Q

What does it mean if the lines are closer to each other on magnetic field lines?

A

Stronger the magnetic field

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16
Q

What is created when a current flows through a wire?

A

Magnetic field - field made up of concentric circles perpendicular to the wire, with the wire in the centre

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17
Q

What happens if you change the driection of the current?

A

It changes the direction of the magnetic field

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18
Q

What is the right-hand thumb rule?

A
  1. Hold your right thumb up
  2. Thumb = direction of current
  3. Fingers = direction of magnetic field
  4. Flip you hand if the current is going downwards
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19
Q

What changes the strength of the magnetic field in a wire?

A
  • Current
  • Distance from wire
20
Q

How can you increase the strength of a magnetic field that a wire produces?

A

Wrapping the wire into a coil called a solenoid

21
Q

What pole is it if the arrowns are pointing inwards?

A

South

22
Q

Describe the MF in a solenoid

A

Strong and uniform (same strength/direction at every point in that region)

23
Q

Ways to increase the strength of a solenoid

A
  • Increase the current that flows through the solenoid
  • Increase no of coils
  • Decrease the length of coils (no of turns is the same)
  • Add an iron core inside the soledoid (become an induced magnet when solenoid is switched on, iron is a soft, magnetic material)
24
Q

What is the MF around a solenoid similar shape to?

A

MF of a bar magnet

25
Q

Uses of electromagnets

A
  • Some cranes - to attract and pick up things made from magnetic materials in scrap yards - magnet can be switched on and off to pick and drop
  • Used within other circuits to act as switches -
26
Q

Why are electromagnets useful?

A

You can change the strength of the MF by changing size of the current + its quick to switch on and off

27
Q

What is the motor effect?

A
  1. When a current-carrying wire (or any conductor) it put between magnetic poles
  2. Magnetic field around wire interacts with magnetic field it has been placed in
  3. Causes the magnet and the conductor to exert a force on each other
  4. Causes wire to move (upwards?)
28
Q

Formula for force from motor effect. What is it only used for?

A

F = BIl
Force = Magnetic flux density (T) X Current (A) X length (m)
Applies to a wire which is at right angles to the MF

29
Q

What is the magnetic flux density?

A

Measure of the strength of the MF/ how many field (flux) lines there are in a region

30
Q

What 3 things affect the force acting on a conductor in a MF

A
  • Magnetic flux density
  • Size of the current through the conductor
  • Length of the conductor thats in the magnetic field
31
Q

Flemings left hand rule

A
  • 1st finger = direction of field
  • 2nd finger = direction of the current
  • Thumb - direction of mvoement
32
Q

How does an electric motor work?

A
  1. A wire with a current in placed in a magnetic field
  2. Wire experiences a force on the right and left sides
  3. Using Flemings left hand rule, you see that the force on the left acts upwards, the force on the right acts downwards
  4. Moments on both sides = loop will rotate in clockwise direction
  5. Stops at 90
  6. Switch direction of current when loop passes 90 by adding split-ring commutator
  7. Commutators swaps the contacts to keep coil rotating in the same direction
33
Q

How to fix an electric motor so it turns 360?

A
  1. Switch direction of current when loop passes 90 by adding split-ring commutator
    2.
34
Q

What is a split ring commutator?

A
  • Split metal ring
  • Connected to conducting brushes
  • Brushes allow current to pass onto the ring
35
Q

What is an electromagnet?

A

A solenoid with an electric core

36
Q

How do headphones work?

A
  1. Circular south pole magnet surrounded by north pole magnet = m.field
  2. Paper cone over south pole wrapped around metal wires
  3. Power on = current in wires = m.field = electromagnetism
  4. 2 m.field interaction = motor effect = force
  5. Force causes paper cone and coil to move up and down
  6. Causes vibrations in the air as comrpessions and rarefractions (sound)
  7. If you change the frequency of the current, it wil alter the sound wave produced
37
Q

When do we only see the generator effect?

A

If the wire passes through the magnetic field

38
Q

Generator effect

When is the induced potential difference and current larger?

A
  • If we use a stronger m.field
  • if we move the wire more rapidly
  • if we shape the wire into a coil (greater No of turns on coil, greater the induced pd and current)
39
Q
  1. What happens when you have magnets with a MF between them and take a wire and move it through the m field?
  2. What if you stop moving it?
  3. What happens to the direction of the pd every time you change the direction?
A
  1. It will induce a potential diff in the wire
  2. The pd disappears because its the change the m field the wire experiences that creates the pd
  3. Direction of pd swaps each time ( plus and minus swap each time)
40
Q

Generator effect

What if you joined the 2 ends to create a complete circuit between the m field?

A
  • Induces pf would generate a current
  • Electrons able to flow around the ciruit
41
Q

Generator effect

What would change the direction of the current in a complete circuit if a magnet is entering the coil?

A

Swapping poles of the magnet (turning it around)

42
Q

What is an alternator?

A
  • They rotate a coil in a magnetic field
  • As the coil spins, a current is induced in the coil - this current changes direction after every half turn
  • ac generators have slip rings and brushes so contacts dont swap every half turn
  • means they produce an alternating pd
43
Q

What do the commutators do in an alternator?

A

allow the current to pass out of the coil

44
Q

What is a dynamo?

A
  • They have split-ring commutator
  • This swaps the connection every half turn to keep the current flowing in the same direction
  • They produce direct current
45
Q

What do split rings help with in alternators?

A

Prevent wires getting tangled

46
Q

What causes a magnet to become demagnetised?

A
  • Heating it
  • Iron atoms vibrate, certain temp, magnetic field stops being aligned in a certain direction
  • Position magnet in a solenoid and pass ac current - current causes MF to constantly change direction, domains become disorganised

Physics - Y10 + Y11 (7 decks)

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