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Physics AQA Triple > Magnetism > Flashcards

Magnetism Flashcards

Paper 2 - P7

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1
Q

What happens when we bring two magnets close to each other?

A

They exert a force on each other

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2
Q

What do two like poles do to each other?

A

They repel each other

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3
Q

What do two unlike poles do to each other?

A

They attract each other

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4
Q

What is the attraction and repulsion between two magnetic poles an example of?

A

Non-contact forces

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5
Q

What is a permanent magnet produce?

A

It’s own magnetic field

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6
Q

What happens if we bring a permanent magnet close to another permanent magnet?

A

They can attract or repel each other depending on the direction.

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7
Q

What is an induced magnet?

A

It is an object that becomes a magnet when it is placed in a magnetic field.

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8
Q

What are the four types of magnetic materials?

A

-Iron
-Steel
-Cobalt
-Nickel

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9
Q

What is a magnetic field?

A

A region around a magnet where a force acts on another magnet or on a magnetic material.

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10
Q

What happens if we place a magnetic material into a magnetic field?

A

If we place a magnetic material such as iron into this field, then it will experience a force of attraction towards the magnet.

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11
Q

What can the direction of a magnetic field be found by?

A

By using a compass

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12
Q

How do we know Earth has its own magnetic field?

A

Because when we hold a compass away from any magnets, then the needle always points in the North-South direction.

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13
Q

What happens when current flows through a conducting wire?

A

A magnetic field is produced around the wire

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14
Q

How can we prove that there is a magnetic field around a wire?

A

By using a compass -> When we turn the current on the compass needle deflects towards the wire.

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15
Q

What does the strength of the magnetic field depend on?

A

-Size of the current
-Distance to the wire
-Direction of current
-If the wire is coiled (solenoid)

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16
Q

How do we work out the direction of the magnetic field produced by a wire?

A

Using the right hand grip rule

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17
Q

How do we use the right hand grip rule?

A

By placing our right hand so that the thumb is pointing in the direction of the conventional current. Now the fingers are pointing in the direction of the magnetic field.

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18
Q

What happens to the magnetic field inside a solenoid when we turn on the current?

A

We get a strong and uniform magnetic field inside the solenoid

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19
Q

What are the three ways that we can increase the strength of the magnetic field produced by a solenoid?

A

-Increasing the size of the current
-Increasing the number of turns of the coil
-If we place a piece of iron inside the solenoid (iron core)

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20
Q

Why are electromagnets useful?

A

As we can change the strength of the magnetic field by changing the size of the current. And we can turn it on or off.

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21
Q

(Triple only) Why are high voltage circuits dangerous?

A

Since they can be turned on and off, they can get sparking and a risk of electrocution.

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22
Q

(Triple only) How can we turn off high voltage circuits?

A

By using a relay

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23
Q

(Triple only) What does a relay contain?

A

Two separate circuits,
-One with a low voltage circuit containing an electromagnet which is safe to be switched on and off.
-And on the high voltage circuit we have replaced the switch with two metal contacts.

24
Q

(Triple only) What are the contacts connected to in a relay?

A

One is connected to the spring which keeps the contacts apart. With an iron block next to the spring.

25
Q

(Triple only) What happens if the low voltage circuit is turned off?

A

No current is flowing through the electromagnet and there is no magnetic field. And the high-voltage circuit is turned off because the contacts are not touching.

26
Q

(Triple only) What happens when the low voltage circuit is turned on?

A

A current now flows around the circuit which means there is now a magnetic field around the electromagnet. The magnetic field now attracts the iron block in the high voltage circuit which causes the contacts to close and switches on the high voltage circuit.

27
Q

(Triple only) How does a doorbell work?

A

-The switch is closed the buzzer is pressed which causes a current to flow through the circuit and a magnetic field is now produced by the electromagnet.
-The iron contact is now attracted towards the magnetic field.
-When the contact moves towards the magnetic field, the clapper now hits the bell. And at the same time, this breaks the circuit.
-Now there is no current flowing, so there is no magnetic field and the iron contact now springs back to its original position.
-Now the circuit is complete again so a current flows around the circuit and the process is repeated.

28
Q

What is meant by the motor effect?

A

A wire carrying a current creates a magnetic field. This can interact with another magnetic field, causing a force that pushes the wire at right angles.

29
Q

What is it meant by the magnetic flux density?

A

A measure of the strength of the magnetic field

30
Q

How do we determine the direction of the force?

A

Using Fleming’s left hand rule. Place your thumb, first finger and second finger so they are at right angles. Now point your first finger in the direction of the magnetic field from North to South. Now point your second finger in the direction in the conventional current. The direction that your thumb is pointing shows you the direction of the motion (force).

31
Q

What happens if the conductor is parallel to the magnetic field in the motor effect?

A

The magnetic field will not experience a force

32
Q

How does an electric motor work?

A

-Current in the left hand part of the coil causes a downward force, and current in the right hand part of the coil causes an upward force.
-The coil rotates anticlockwise because of the forces.
When the coil is vertical, it moves parallel to the magnetic field, producing no force.

This would tend to make the motor come to a stop, but two features allow the coil to continue rotating:

-The momentum of the motor carries it on round a little
a split ring commutator changes the current direction every half turn.

Once the conducting brushes reconnect with the commutator after a half turn:

-Current flows in the opposite direction through the wire in the coil.
-Each side of the coil is now near the opposite magnetic pole.

33
Q

What is a split ring commutator?

A

Part of a dc electric motor that reverses the direction of the current every half turn of the coil. So that the forces on the loop always keep acting in a way to keep the loop rotating.

34
Q

What is a DC motor?

A

An electrical device that uses direct current to produce a turning effect.

35
Q

What happens if we switch the direction of the current in an electric motor?

A

The split ring commutator allows the motor to keep rotating in the same direction.

36
Q

(Triple only) How does a moving-coil loudspeaker work?

A

-We have a cone which has a coil of wire wrapped around one end.
-The coil of wire is connected to an AC electrical supply.
-We also have a permanent magnet which goes inside the coil of wire.
-As the current passes through the coil, it generates a magnetic field, this now interacts with the magnetic field from the permanent magnet and these magnetic either attract or repel each other.
-This produces a resultant force which causes the cone to move.
-When the current switches direction, the direction of the force on the cone reverses which causes the cone to move in and out, generating sound waves.
-By changing the frequency of the AC supply, we can change the frequency that the cone vibrates.

37
Q

(Triple only) What happens if we increase the size of the current in a loudspeaker?

A

Then we increase the amplitude of the vibration which increases the volume of the sound.

38
Q

(Triple only) What is the induced potential?

A

When the potential difference has now reversed direction.

39
Q

(Triple only) What is the generator effect?

A

When an electrical conductor moves relative to a magnetic field or if there’s a change in the magnetic field around a conductor.

40
Q

(Triple only) How does he generator effect work?

A

The induced voltage produces an induced current if the conductor is connected in a complete circuit. As with all currents, the induced current creates a magnetic field around itself. Note that this magnetic field opposes the original change. For example, if a magnet is moved into a coil of wire, the induced magnetic field tends to repel the magnet back out of the coil. This effect occurs whether a magnet is moved into a coil, or a coil is moved around a magnet.

41
Q

(Triple only) What are the factors that increase the induced potential difference?

A

-If we use a stronger magnetic field
-If we move the wire more rapidly
-If we shape the wire into a coil (The greater the number of turns on the coil then the greater the induced potential difference and current)

42
Q

(Triple only) What are the factors that the induced potential difference depend on?

A

-The magnet is moved out of the coil
-The other pole of the magnet is moved into the coil

43
Q

(Triple only) How does a moving coil microphone work?

A

-We have got a coil of wire attached to a thin sheet of plastic called a diaphragm. The end of the coil of wire sits over a permanent magnet.
-When soundwaves hit the diaphragm, they cause it to vibrate. Now the coil of wire moves in and out through the magnetic field.
-This induces a potential difference across the ends of the wire.
-The potential difference switches direction as the coil moves backwards and forwards through the magnetic field.
-And the frequency of the changing potential difference is the same as the frequency of the sound waves.
-The changing pattern of the potential difference is now passed through an amplifier and then into a moving-coil loudspeaker. This massively increases the volume of the sound.

44
Q

(Triple only) What is a transformer made up of?

A

-Primary coil
-Secondary coil
-Iron core

45
Q

(Triple only) Why is an iron core used in a transformer?

A

Because its easily magnetised

46
Q

(Triple only) How does a transformer work?

A

-As the current flows through the primary coil, it generates a changing magnetic field. This magnetic field is transmitted along the iron core and passes through the secondary coil.
-When the changing magnetic field passes through the secondary coil, it induces a potential difference.

47
Q

(Triple only) Why do transformers only work with alternating current (AC)?

A

That is because we need a changing magnetic field to induce a potential difference and a direct current (DC) produces a constant magnetic field and therefore it does not work in transformers.

48
Q

(Triple only) What does the iron core increase?

A

Strength of the magnetic field

49
Q

(Triple only) What is a step-up transformer?

A

Steps up the voltage and consequently steps down the current.

50
Q

(Triple only) What is a step-down transformer?

A

Reduces the potential difference

51
Q

(Triple only) How is electrical power transmitted from power station to homes?

A

Through high-voltage cables

52
Q

(Triple only) What happens if we want to transmit a large amount of power?

A

We can use a large current or large voltage

53
Q

(Triple only) What is the problem with transmitted cables?

A

Power is wasted in the transmission cables as heat and the amount of power wasted as heat depends on the square of the current.

54
Q

(Triple only) What happens if we use a large current in the transmission cables?

A

A huge amount of power would be wasted as heat so we use a large potential difference instead.

55
Q

(Triple only) What is the process in which electricity goes from the power station to homes?

A

-The electricity from the power station is first passed through a step-up transformer which steps up the potential difference to around 400 000 V.
-The electrical power is then transmitted down high-voltage cables.
-It is then passed through step-down transformers which reduce the potential difference to around 230 V.
-Then it is passed into homes.

56
Q

(Triple only) Why are transformers useful?

A

Because they massively reduce power wastage in the National Grid

Physics AQA Triple (8 decks)

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