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Physics paper 2 > SP12 and 13 > Flashcards

SP12 and 13 Flashcards

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1
Q

What happens to unlike magnetic poles?

A
  • They attract
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2
Q

What happens to like magnetic poles?

A
  • They repel
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3
Q

What is a permanent magnet?

A
  • A magnet that is always magnetic and cannot be turned on and off
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4
Q

What is an induced magnet?

A
  • A magnet that can be turned off and on and is only magnetic when placed inside a magnetic field
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5
Q

What are some uses of magnetic materials?

A
  • Compasses
  • Motors
  • Knife holders
  • Loudspeakers
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6
Q

Which way do arrows point in a magnetic field when drawing lines?

A
  • Field lines go in from the South pole and out from the North pole
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7
Q

How do field lines show strength of a magnetic field?

A
  • When field lines are denser (more close together), the field is stronger
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8
Q

How can plotting compasses be used to show shape of magnetic field?

A
  • The tiny bar magnet points in the direction of the magnetic field, which can show the direction of the field at different points around a magnet
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9
Q

How do compasses show that the Earth’s core is magnetic?

A
  • The tilt by different amounts, relative to the horizontal. This shows how the magnetic field of the Earth causes a shift in the compass position
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10
Q

What is the shape of the magnetic field produced when a current is passed through a wire?

A
  • Magnetic field made of multiple circles around each other, closest together nearest to the wire
  • The ‘Right hand grip’ rule can be used to how the direction of the field compared to the current flow
  • As distance from the wire increases, the strength of the magnetic field decreases
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11
Q

What is a solenoid and describe the magnetic field in it?

A
  • A solenoid is a series of coils of wire, one after the other
  • The magnetic field is strong and uniform within a solenoid, because they add together
  • The magnetic field is weaker on the outside as they cancel each other
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12
Q

What are four ways of increasing the strength of an electromagnet?

A
  • Increase the current flowing through the solenoid
  • Increase the number of turns (or coil) in the solenoid
  • Decrease the length of the solenoid, whilst keeping number of turns the same
  • Add a soft iron core in the middle of the solenoid
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13
Q

What happens when a current carrying conductor is placed near a magnet?

A
  • It experiences a force, whilst an equal and opposite force acts on the magnet (this is known as the Motor Effect)
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14
Q

How does a magnetic force occur?

A
  • It is due to interactions between magnetic fields, where it will either cause attraction or repulsion
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15
Q

What is Fleming’s left-hand rule?

A
  • A method of determining the force on a conductor carrying a current
  • Can be done by holding your left hand, with the first three fingers at right angles from each other
  • The direction of the thumb represents Force, the index finger represents the Magnetic field and the middle finger represents the Current
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16
Q

How do you calculate the strength of the force?

A

F = B x I x L
- F= force and is measured in Newtons (N)
- B=magnetic flux density and is measured in Teslas (T)
- I= current and is measured in Amperes (A)
- L=length and is measured in metres (M)

17
Q

How does an electric motor spin?

A
  • There is a magnetic field caused by two magnets on either side of the motor
  • There is a current flowing through the motor, which flows in opposite directions at either end
  • Due to Fleming’s left-hand rule, each side of the motor will experience an opposite force, causing it to spin clockwise
18
Q

What is the role of a split-ring commutator?

A
  • Every 180 degrees that the motor turns, the currents will now be facing in opposite directions, resulting in the forces acting in opposite directions and the motor turning anticlockwise
  • To overcome this, a split-ring ring commutator swaps the positive and negative connections every half-turn, allowing the currents to swap so that the motor can turn a full 360 degrees as the forces will always act in the same direction
19
Q

What are 3 ways of increasing the speed of rotations in a motor?

A
  • Increase the current
  • Increase the number of coils
  • Increase magnetic flux density by increasing magnet strength
20
Q

What is electromagnetic induction?

A
  • The effect seen as the movement of a wire or magnet in a field will induce a voltage
  • Each time direction changes, the direction of the potential difference changes
21
Q

What factors affect the size of the induced potential difference- and therefore the current?

A
  • Change strength of magnetic field by using stronger magnets
  • Move wire/magnets quicker, to faster change the field
  • Shape wire into a coil, as more turns mean an increased potential difference
22
Q

What factors affect the direction of the potential difference?

A
  • Direction by which magnet-wire is moved into/out of the field
  • Direction of poles in the magnet
23
Q

How does a generator produce an alternating current?

A
  • Consists of a coil of wire rotated inside a magnetic field
  • As the coil rotates, a potential difference is induced
  • The coils are connected to slip rings, which come into contact with carbon brushes, which press on them and allow a current to flow
  • These types of generators are called alternators
24
Q

How does a generator produce a direct current?

A
  • It uses a split-ring commutator, which switches the connections every half-turn and allows a direct current to flow
  • This is known as a dynamo
25
Q

How does a microphone work?

A
  • A person singing causes sound waves and air pressure that hit the diaphragm and causes vibrations
  • This causes the coil of wire within the microphone to move backwards and forwards
  • This results in electromagnetic induction, causing a current and allowing the signal to be amplified
26
Q

How does a loudspeaker work?

A
  • Similar to microphone, yet it starts out with current and ends with air pressure
  • An alternating current and magnetic field within the speaker causes a force to be achieved (Fleming’s left-hand rule)
  • The AC means the force moves backwards and forwards, causing a paper cone to do so too, causing vibrations and amplifying the noise
27
Q

What is the role of a transformer?

A

To increase (step-up) or decrease (step-down) the size of an alternating voltage

28
Q

How does a transformer work?

A
  • An alternating potential difference is applied across the primary coil, causing a current to flow and generate a magnetic field around the coil
  • This induces an alternating magnetic field in the iron core
  • This induces a potential difference in the secondary coil
  • If this is part of a complete circuit, it causes current to flow
29
Q

How does a transformer step-up or step-down the voltage?

A
  • By increasing or decreasing the number of turns in the secondary coil, it increases or decreases the potential difference, respectively
30
Q

Why and where are transformers used?

A
  • An increase in voltage means that the wire gets hitter, and so more energy is lost through heating
  • Transformers step down the voltage before entering a transmission line, to reduce energy lost as electricity travels over a long distance
  • They then step up the voltage at the end, so more electricity can travel to homes and power buildings
31
Q
A

Physics paper 2 (6 decks)

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