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GCSE Physics OCR A > P4 > Flashcards

P4 Flashcards

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1
Q

What is a force?

A

A push/pull

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2
Q

How does the distance affect force?

A

All three get smaller as you move further away from the mass/magnet/charge

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3
Q

Describe magnet

A

An object with a magnetic field
Exert a force on a magnetic material

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4
Q

How do field lines reflect the magnetic strength?

A

The more denser the field lines are , the stronger the magnetic field

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5
Q

What are permanent magnets?

A

Always has a magnetic field
Attract/repel other permanent magnetic and also non magnets

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6
Q

How do permanent magnets exert a force on non-magnet?

A

When brought close , non magnets have magnetism induced in them.

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7
Q

What direction do magnetic field lines go in?

A

From North Pole to South Pole

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8
Q

Describe the 🌎’s magnetic field

A

The geographic North Pole is the magnetic South Pole.
Because the magnetic north Pole points to the geographic south Pole

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9
Q

What happens when two magnetic fields interact?

A

The lines will best around
Creating a high density of field lines between the two magnets, however weak in other places (weak attraction)

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10
Q

What happens when current flows in a wire?

A

A magnetic field is generated around it

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11
Q

What is a magnetic field?

A

A region of space within which a magnet experiences a magnetic force of attraction or repulsion.

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12
Q

Describe the look of magnetic fields exist around wires?

A

Concentric rings
The space between the lines increases with increasing distance

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13
Q

How does a stronger current affect the magnetic field?

A

Stronger magnetic field
the space between the lines are smaller

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14
Q

What is the corkscrew rule?

A

RIGHT HAND
Thumb = direction of current
Fingers= direction of magnetic field

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15
Q

What is a solenoid?

A

A device that increases the strength of the magnetic field around a current carrying wire

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16
Q

How do you make a solenoid?

A

A wire wrapped many times around a metal that can be magnetised
*not permanent magnets

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17
Q

What is an electromagnet?

A

A magnet which runs on electricity, the field can be switched on and off

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18
Q

What effects the strength of a solenoid?

A

🧲coils in the wire
🧲size of current
🧲material of the core inside the wire

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19
Q

How would you show there is a field around a solenoid?

A

Use iron fillings

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20
Q

What is the relationship between the distance and the strength of a wire?

A

inversely proportional
The strength is the square of the distance
Eg: double distance , strength decreases by a factor of 4

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21
Q

What is magnetic flux density?

A

The number of lines of force passing though a unit of area of material
Measured in Tesla’s
Newton per amp meter

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22
Q

What does a circle with an x mean ?

A

The arrow is going into the page

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23
Q

What does a circle with a point mean?

A

The arrow is coming towards me

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24
Q

How do you calculate the force on the conductor?

A

F = BIL
F= force (N)
B= magnetic flux density (T)
I= current (A)
L= length of conductor (m)

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25
Q

What does Flemings left hand rule state ?

A

The direction of force exerted is always perpendicular to both the direction of the magnetic field and the direction of the current in the wire.

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26
Q

How do you use Fleming’s left hand rule?

A

Thumb =force
First finger= field
Second finger =current
FFC

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27
Q

What does an electric motor do?

A

Uses the motor effect to transfer electric energy to kinetic energy

28
Q

What does an electric motor consist of?

A

A loop of wire , with a current in a magnetic field

29
Q

Why must the current be reversed every half turn?

A

If the current was not reversed , the direction would be (force).
Causing it to spin anti clockwise and then clockwise,
Shaking and flopping -not turning

30
Q

What does a split ring commutator do?

A

Reverse the direction of the current every half turn.
Allowing the coil to rotate in the same direction

31
Q

Why does increasing the current increase the force ?
( motor effect )

A

1.Magnetic field lines exist around a wire with a current
2. The larger the current the greater magnetic fie,s strength in the interaction between the wire and permanent magnet

32
Q

Why would some motors use electromagnets rather than permanent?

A

Electromagnets produce stronger fields

33
Q

Describe the motor effect :

A

🔘a looped wire carrying current is placed within a magnetic field
🔘therefore the wire experiences a force, causing it to turn
🔘to make it spin the same direction a split ring commutator is required to reverse the current every half turn
🔘this allows the loop to spin in one direction
🔘as it spins electrical energy is transferred to kinetic energy

34
Q

What is an electrostatic field in motion?

A

A magnetic field

35
Q

How do you draw a magnetic field around current carying wires?

A

Use the right hand corkscrew rule.
The direction the thumb points in is the North Pole

36
Q

How do you draw a magnetic field around a solenoid?

A

Use the right hand corkscrew rule, but align your fingers with the coils (thumb points to the North Pole).
Draw as a bar magnet
*but the strength of the field lines is now greatest in between the coils

37
Q

Why does a current carrying wire have a magnetic field?

A

The electrons within the wire have an electrostatic field, as they move the electro static field is in motion creating a magnetic field

38
Q

What is a magnetic field?

A

An electrostatic field in motion

39
Q

What is the generator effect (electromagnetic induction)?

A

When a conductor cuts the magnetic field lines of a magnet, a potential difference is induced across the ends of the conductor

40
Q

Describe the generator effect:

A

🟣wire with no current , within a magnetic field is experiencing a force
🟣this force is perpendicular to the direction of magnetic field
🟣as the wire cuts field lines, electrons are accelerated inducing a p.d
🟣this creates a current

41
Q

What happens when the motor and generator effect take place together?

A

The force and current produced by the motor effect counteracts the generator effect.(law of conservation of energy)

42
Q

How do you increase the size of the generated p.d?

A

F= increase the velocity/accelerate the wire
B= increase the magnetic field strength (bring closer/new magnets
L= increase the coils on the wire

43
Q

What happens when you reverse the direction of the wire in the generator effect?

A

The direction of p.d is reversed
(Negative p.d)

44
Q

How does a stronger magnetic field produce a larger current in the generator effect?

A

The stronger the magnetic field, the more dense the field lines are , the rate at which magnetic field lines are cut is faster, larger current

45
Q

State Lenz’s Law

A

The direction of the induced p.d is such that it opposes the change producing it

46
Q

How can you use the generator effect to slow down a falling lift (no cable) ?

A

🔴a lift with permanent magnets, inside a metal tunnel
🔴as the loft falls , magnets move past the metal surfaces of the tunnel
🔴the lifts (metal surfaces), will cut the magnetic field lines , inducing a p.d and current within
🔴the current carrying surface will interact with the magnetic field of the tunnel giving rise to a force in the opposing direction (motor effect)
🔴this force will counteract the weight force of the falling lift , causing it to fall slower🔴

47
Q

What does a voltage time graph look like for a generator?

A

A sin graph.
*the highest peaks are for when the field lines were cut and the closest angle (90°)

48
Q

Describe the alternator

A

*generator affect
Produced a.c (magnetic field lines as cut from above and below
Uses a slip ring(doesn’t change direction of the current)

49
Q

Describe a dynamo

A

*generator effect
Produces d.c
Split ring (reverses the current every half turn)

50
Q

How do you increase the induced p.d of an alternator?

A

🟣rotate coil faster (more field lines cut per second)
🟣stronger magnetic field (field lines closer together, so more cut)
🟣more coils
* doubling frequency

51
Q

Compare dynamos and alternators

A
52
Q

What are transformers?

A

Devices that use a.c in the primary circuit to induce an a.c in the secondary current

53
Q

How do transformers work?

A
54
Q

How do transformers work?

A
55
Q

Describe the difference between step up and step down transformers

A
56
Q

What is the transformer equation?

A
57
Q

How do microphones work?

A

🟢generator effect
🟢sound waves hit diaphragm, causing it to move forwards and backwards
🟢so the coil attached also moves backwards and forwards
🟢the coil moves inside a magnetic field , so cuts field lines perpendicularly
🟢a p.d is now induced within coil, producing an electrical signal fed to a speaker

58
Q

How do loudspeakers work?

A

🟢a current carrying wire, enters a magnetic field . MOTOR EFFECT. This causes the wire to experience a force
🟢as the coil moves forwards and backwards, the diaphragm moves forwards and backwards
🟢therefore creating sound waves , at the same frequency diaphragm vibrates

59
Q

Describe the circular magnet
In loudspeakers,
The charge

A
60
Q

Draw the magnetic field around a solenoid

A
61
Q

Describe electromagnet induction:

A

A chaos in the magnetic field around a conductor can give rise to an induced potential difference across it’s ends , which could drive a current , generating a magnetic field that would pose the original change

62
Q

What is happening in the photo

A

Moving magnet = changing magnetic field
Induces a p.d in coils
Magnetic field of coil(wires) is produced due to current
The North Pole will be generated on left hand side to oppose the original magnetic field (Lenz’ law)
Repelling

63
Q

What is happening in the photo

A
64
Q

What are some ways to produce a changing magnetic field ?

A
65
Q

How do transformers work?

A
  1. Alternating p.d across the primary coil produces an alternating current in the primary coil
  2. An alternating current produces in the primary coil produces a magnetic field in the iron core that is always changing
  3. This induced a changing p.d in the secondary coil
66
Q

How do dynamic microphones work?

A

Sound waves are pressure waves.
Areas of high pressure (compression ) push the diagram in
Areas of low pressure (rarefactions ) pull diagram in.
Coil moves in and out in magnetic field, inducing p.d across ends of wire

GCSE Physics OCR A (13 decks)

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