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GCSE Physics > Magnetism and Electromagnetism > Flashcards

Magnetism and Electromagnetism Flashcards

1
Q

What is a magnet?

A

any material or object that produces a magnetic field

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2
Q

What direction do field lines go in?

A

north to south

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3
Q

How do field lines show field strength?

A

denser lines show a stronger field

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4
Q

What are the 2 types of magnets?

A

permanent, induced

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5
Q

What is the difference between a magnet and a magnetic material?

A

magnet actually produces a magnetic field
magnetic material can be influenced by magnetic field and has potential to become a magnet

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6
Q

What are the 3 main magnetic element?

A

nickel cobalt iron (+ steel)

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7
Q

What is the difference between an induced and a permanent magnet?

A

permanent always produce their own magnetic field
induced have a magnetic field temporarily

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8
Q

How are induced magnets created?

A

when magnetic material - that isn’t magnetised - gets put into the magnetic field of a permanent magnet. This causes it to develop its own north and south pole.

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9
Q

True or False: An induced magnet will always be attracted to the permanent magnet.

A

true

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10
Q

What is magnetically soft or hard?

A

magnetically soft materials lose their magnetism fairly quickly. (e.g. iron)
magnetically hard materials lose their magnetism much more slowly. (e.g steel)

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11
Q

what is electromagnetism?

A

the phenomenon in which electric currents produce their own magnetic fields

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12
Q

What is the right hand rule?

A

a way of showing the direction of the magnetic field in a wire.
your thumb is the direction of current and the direction your fingers wrap around is the direction of the magnetic field

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13
Q

What is a solenoid?

A

a magnet created by passing current through a coil of wire

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14
Q

what are 4 ways to increase an electromagnet’s strength?

A

increase current
increase number of coils
decrease the length of coils (denser coils)
Add an iron core to the inside of the solenoid

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15
Q

What is the motor effect?

A

when a current carrying wire is placed within a magnetic field, the two magnetic fields will interact and the wire will experience a force.

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16
Q

What is Fleming’s left hand rule?

A

index finger straight, showing magnetic field
middle finger perpendicular, showing current
thumb point up, showing force

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17
Q

What is the equation to work out the strength of the force in the motor effect?

A

force = magnetic flux density * current * length of wire (m)

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18
Q

What are the units of magnetic flux density?

A

tesla

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19
Q

How can you ensure that the wire experiences the full force in the motor effect?

A

make sure the wire is perpendicular to the magnetic field

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20
Q

What does a split ring commutator do?

A

swaps the positive and negative connections every half turn, which swaps the direction of the current

21
Q

Why is a split ring commutator used?

A

to swap the current every half turn and keep the wire rotating in the same direction.

22
Q

What would happen to the motor if a split ring commutator was not used?

A

the wire would turn 180 then turn back and keep oscillating till eventually it stops vertically.

23
Q

How can you increase speed of rotations in a motor?

A

increase current
add more turns to the coil
increase magnetic field strength

24
Q

What is the generator effect?

A

when you move a wire through a magnetic field, a potential difference will be induced in the wire

25
what is needed to generate current in the wire in the generator effect?
a complete circuit
26
How could you change the size of the p.d. induced in the generator effect?
Change strength of magnetic field move wire or magnets faster shape the wire into a coil and increase the turns to get a bigger p.d.
27
Why does the direction of the current repeatedly change in the generator effect?
when the wire moves in one direction a current is produced, but when its stopped and moved back, it generates an opposite current. As it keeps oscillating, alternating current is produced
28
Will a wire moving parallel or moving perpendicular to the magnetic field generate a p.d.?
perpendicular
29
What are the 2 types of generators and what current do they generate?
alternators (ac) dynamos (dc)
30
What is the difference between and alternator and a dynamo?
dynamos have a split ring commutator alternators have slip rings and brushes
31
How do alternators work?
the coil of wire rotates inducing a voltage and current in the coil the slip rings and brushes mean that the contacts don't swap every half turn this produces and alternating current
32
What effect does rotating the coil faster have on current in an alternator?
the current increases and alternates quicker
33
How do dynamos work?
when the coil of wire spins, a current is induced the split ring commutator means that the contacts swap every half turn this produces a direct current
34
What effect does rotating the coil faster have on current in a dynamo?
the current increases and is more stable
35
what effect do loud speakers use to convert from electrical signals to sound?
motor effect
36
what effect do microphones use to convert sound to electrical signals?
generator effect
37
what type of current is involved in both microphones and loudspeakers?
alternating current
38
what is a loud speaker made up of?
A loudspeaker consists of a coil of wire which is wrapped around one pole of a permanent magnet and connected to a cone. The coil of wire is permanently attached to the cone, but the coil and cone can slide back and fourth along the magnet.
39
How do loudspeakers work?
1) a.c. flows though the coil of wire and creates magnetic field 2) magnetic field interacts with permanent magnetic field exerting a force on the coil causing it to move back and forth along the permanent magnet 3) as the current is alternating, the magnetic field and force also alternates, meaning it vibrates 4) these vibrations are so fast, they can cause pressure variation in the air which is sound waves
40
What is a microphone made up of?
A microphone consists of a coil of wire which is wrapped around one pole of a permanent magnet and connected to a diaphragm. The coil of wire is permanently attached to the diaphragm, but the coil and diaphragm can slide back and fourth along the magnet.
41
How do microphones work?
1) sound waves hit the diaphragm causing it to and the coil of wire to move 2) as the wire moves within the permanent magnet's magnetic field, it generates a current (generator effect) 3) the frequency and amplitude of the sound waves determines how much the diaphragm vibrates and therefore the frequency and amplitude of the current
42
How are transformers used in the national grid?
step up transformer used to increase the voltage from power stations to around 400,000V in order to decrease energy loss as the electricity travels through wires and pylons step down transformers used to decrease the voltage to around 230V allowing it to be safely used in households.
43
How do transformers work?
1)there is an alternating p.d. and current flowing through the primary coil, creating an alternating magnetic field 2) the iron core gets magnetised and also has an alternating magnetic field 3) the iron core's magnetic field induces a p.d in the secondary coil and if it is part of a circuit, current will flow.
44
why cant the electricity just pass from the primary coil to the secondary coil via the iron core?
the coils are insulated in plastic
45
why is electromagnetism used in transformers?
it allows for us to change the size of the p.d. between the two coils
46
what is the relationship between the number of coils and p.d. in the 2 coils?
it is directly proportional, so if the secondary coil has twice as many coils as the primary coil, the p.d. will be double
47
what type of current is required for transformers to work?
alternating
48
48
what are the 2 transformer equations?
V(p) / V(s) = n(p) / n(s) V(p) * I (p) = V(s) * I (s) p= primary coil s= secondary coil V= voltage I= current n= number of coils

GCSE Physics (9 decks)

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