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Physics - PAPER 2 > Magnetsim And Motors > Flashcards

Magnetsim And Motors Flashcards

1
Q

What is a permanent magnet?

A

A magnet that is always magnetic e.g bar magnet

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2
Q

What does the north side of the magnet attract?

A

The south side

Another north would repel

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3
Q

What is an induced magnet?

A

When a magnetic material is in a magnetic field, it becomes a magnet itself
However, it stops being magnetic once removed from the field

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4
Q

How can the shape of magnetic fields be found?

A

Plotting compasses

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5
Q

What are two features of bar magnets? | ——- |

A

Has the same strength and direction anywhere

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6
Q

What does the arrow on a plotting compass point to?

A

A position by the Earth’s North Pole

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7
Q

What is a magnetic North Pole?

A

Defined in terms of the direction of the magnetic field lines, so the magnetic pole in the northern hemisphere, is actually a south magnetic pole

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8
Q

What is this evidence of?

A

That the earth has a magnetic field

Which is thought to be caused by electric currents in the molten core

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9
Q

How do you find the direction of magnetic field?

A

You take right hand and point thumb in direction of current. The curve of your fingers shows the direction of magnetic field

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10
Q

How is the strength of the magnetic field depending on the size of the current?

A

The higher the current, the stronger the field.

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11
Q

Where is the magnetic field strongest?

A

Closer to the wire and gets weaker when distance from wire increases

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12
Q

What is a solenoid?

A

Wire made into a coil

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13
Q

Why is there a weaker field outside the solenoid?

A

The fields from one side of the coil tend to cancel out the fields from the other side

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14
Q

Why is there a stronger field inside the solenoid?

A

The fields from individual coils add together

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15
Q

What is an electromagnet?

A

A coil of wire with a current flowing in it

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16
Q

How can you increase the strength of the magnetic field?

A

An iron core - becomes a temporary magnet

17
Q

How do you change the direction of the field?

A

You change the direction of the current

18
Q

How do you strengthen the field?

A

Increase the current

19
Q

What is fleming’s left hand rule?

A

Thumb = movement
1st finger = field from north to south
2nd finger = current (+ to -)

20
Q

How do you calculate the force in conductor?

A

Force in conductor
carrying current at = magnetic flux x current x length
right angles to density (A) (m)
magnetic field (T)
(N)

21
Q

What is he force in conductor in a magnetic field used for?

A

To cause rotation in electric motors
There is a force on each part of the wire carrying a current in the magnetic field so using a coil with many turns of wire, increases the total force which turns the coil

22
Q

What do the carbon brushes do?

A

Make electrical contacts between the circuit and the motor

23
Q

What does the metal split-ring commutator do?

A

Ensures the force on coil is always turning it in the same direction

24
Q

What happens when a magnetic field is changing?

A

It induces a potential difference in a wire which causes a current to flow

25
Q

What does the size of the induced potential difference depend on?

A

The number of turns in a coil of wire
Strength of magnetic field
How fast the magnetic field changes/moves last the coil

26
Q

What happens when you reverse the direction of the change?

A

Reverse the direction of the induced potential difference

27
Q

What happens when the potential difference causes a current to flow?

A

The magnetic field of the current opposes the original change

28
Q

What is generator and how does it work?

A

Consist of a coil of wire that is rotated inside a magnetic field
As the coil turns, a voltage is induced in the wire
The ends of the coil are connected to slip rings
Electrical contact with external circuit is made using carbon brushes which press on the slip rings
Produces an alternating current

29
Q

How do microphones convert sound waves into electrical signals?

A

The sound waves cause variations in air pressure
The pressure variations make a diaphragm vibrate
The diaphragm moves a coil of wire backwards and forwards creating the electrical signals

30
Q

How do loudspeakers convert electrical signals into sound waves?

A

The varying current flows through a coil that is in a magnetic field
This caused a force on the coil which moves backward and forwards as the current varies
The coil is connected to a diaphragm, and the movements of the diaphragm produce sound waves

31
Q

What is a transformer?

A

Made using two coils of insulated wire wound onto an iron core
(No electrical connection between the two coils of wire)

32
Q

What is the National Grid?

A

Power stations produce a 25kV voltage which is increased to 400kV by transformers to reduce energy lost by heating.
The transmission lines take the voltage to new transformers where they reduce it to 33kV or 11kV for factories.
The rest is taken to another transformer which reduced us to 230V as it is a safe amount, and this is for homes and shops

33
Q

What current do a transformer need to work?

A

An alternating current as the P.D changes many times a second

34
Q

What does the alternating current in the primary coil create?

A

A constantly changing magnetic field which is taken to secondary coil via the iron core

35
Q

What does the magnetic field induce?

A

A changing potential difference in the secondary coil

It is greater if it has more turns than the primary coil

36
Q

How do you work out the P.D or number of turns in the primary and secondary coils?

A

Potential difference Number of turns in the
across primary coil primary coil
————————. = ——————————-
P.d across the Number of turns in the
Secondary coil secondary coil

37
Q

How do you calculate electrical Power?

A

Electrical power = current x potential difference

38
Q

How do you work out electrical power (resistance)?

A

Electrical power = current squared x resistance

Physics - PAPER 2 (5 decks)

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