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physics > magnetism + electromagnetism > Flashcards

magnetism + electromagnetism Flashcards

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1
Q

In induced Magnete, what do the materials not have?

A

Fixed poles.

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2
Q

How can materials be made into temporary magnets?

A

By being ‘stroked’ with a permanent magnet.

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3
Q

How does stroking a material with a permanent magnet make it a temporary magnet?

A

As it aligns the domains in the material in all the same direction.

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4
Q

What does current produce around a wire?

A

A magnetic field.

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5
Q

What rule determines the direction of current?

A

The right hand grip rule.

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6
Q

Which finger points in the direction of the current in the ‘right hand grip rule’?

A

Thumb.

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7
Q

What does every other finger in the ‘right hand grip rule’ represent?

A

The direction of the field.

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8
Q

The greater the current…

A

The stronger the magnetic field.

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9
Q

The greater the distance from the wire…

A

The weaker the field.

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10
Q

Coiling the wire in a solenoid causes…

A

The field to align and form one giant field.

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11
Q

Why does the iron core in the centre of the solenoid increase its strength?

A

As it is easier for magnetic field lines to pass through in comparison to air.

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12
Q

What are 5 factors that affect strength?

A

~Size of current
~Length
~Cross sectional area
~Number of coils
~Soft iron core

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13
Q

In the motor effect, a magnet and a wire will also exert a force as…

A

The two magnetic fields generated by the magnet and the current in the wire interact.

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14
Q

What shape is the magnetic field around a wire?

A

Circular.

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15
Q

What shape is the magnetic field between two magnets?

A

Straight.

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16
Q

How does the conventional current move in Fleming’s left hand rule?

A

Moves in the opposite direction to the electrons.

17
Q

How do you calculate force using magnetic flux density?

A

Force = magnetic flux density x current x length

18
Q

What is magnetic flux density measured in?

A

Tesla and is the number of flux lines per metre squared.

19
Q

How do permanent magnets lie in electric motors?

A

In fixed positions.

20
Q

What is between the permanent magnets in an electric motor?

A

A coil of current carrying wire lies on an axis.

21
Q

Why does an electric motor rotate?

A

Force on one side moves that side up and force on the other side (where current flows in the opposite direction) moves down.

22
Q

When is a potential difference induced across the conductor?

A

When there is a relative movement between a conductor and a magnetic field.

23
Q

A current flows if the conductor forms…

A

A complete circuit.

24
Q

When the current prod yes its own magnetic field, it opposes…

A

The change inducing it.

25
Q

When the turbine spins in an electric generator, the movement causes…

A

The wire to cut through the magnetic field and creates a potential difference.

26
Q

When does an AC flow in an electrical generator?

A

When the coil of wire is connected to a complete circuit.

27
Q

When is a DC produced in an electric generator?

A

If the ends are connected to a split ring commutator.

28
Q

What does a split ring commutator reverse and why?

A

The current each half - rotation so the current remains positive (dynamo system).

29
Q

What is produced when the cone moves in a loudspeaker?

A

Pressure variations which make sound.

30
Q

What interacts in loudspeakers causing the coil to move?

A

The magnetic fields from the current and the magnet.

31
Q

What is the current produced in dynamic microphones proportional to?

A

The sound signal.

32
Q

What is at the centre of a dynamic microphone?

A

A fixed magnet with a coil of wire around it that is free to move.

33
Q

Pressure variations in sound waves in dynamic microphones cause…

A

The coil to move and current is induced as it moves.

34
Q

More coils on the secondary in transformers means…

A

It is a step up transformer as voltage will increase as the changing field will cut through more of the secondary wire inducing a larger potential difference.

35
Q

Fewer coils on the secondary in transformers means…

A

It is a step down transformer as a smaller potential difference forms.

36
Q

Number of coils on primary
——————————————- =
Number of coils on secondary

A

Pd of primary
———————
Pd of secondary

physics (7 decks)

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