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Physics > Electromagnetism > Flashcards

Electromagnetism Flashcards

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1
Q

What does a magnetic field that changes in time create?

A

An induced electric field (emf)

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2
Q

If there are free charge carriers, and induced emf will cause…

A

an induced current to flow.

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3
Q

How does an induced current flow?

A

Such that it opposes the change in the magnetic flux that created it.

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4
Q

A generator converts…

A

Kinetic energy to electrical potential energy

GKE

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5
Q

How does a generator induce emf across the coils to drive a current?

A

It uses the relative movement of the coils of wire and magnets.

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6
Q

What does a transformer do?

A

Acts to change the magnitude of an AC potential difference.

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7
Q

A motor converts…

A

Electrical potential energy to kinetic energy

MEK

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8
Q

How does a motor produces force on the coil?

A

A current flowing through the coil in a magnetic field.

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9
Q

What is the net force on the coil in a motor

A

Zero

The two sides cancel each other out.

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10
Q

What does a DC motor use to change the currents direction every half turn?

A

A commutator

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11
Q

What is a armature?

A

The frame of the rotating part of the motor or generator, holding one or more coils.

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12
Q

What is a diode?

A

A circuit component that allows current to flow in only one directions.

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13
Q

What is an eddy current?

A

A circular current that is induced in a conductor due to a changing magnetic field.

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14
Q

What is electromagnetic induction?

A

The production of an emf due to a time-varying magnetic field.

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15
Q

What is magnetic braking?

A

Bra King due to the interaction of eddy currents and an external magnetic field.

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16
Q

What is magnetic flux?

A

The magnetic field passing through a given area.

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17
Q

What is a rectifier?

A

A circuit that uses diodes to convert AC to DC.

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18
Q

What is rms?

A

The average AC potential difference or current that produces the same power in a load as a DC potential difference or current of the same magnitude.

19
Q

Explain the difference between AC and DC generators?

A

AC provides an alternating current

DC provides a smooth output.

20
Q

Why does the current of a DC motor need to be reversed every half turn?

A

If the direction of current is not reversed, then every half turn the directions of the forces on the sides of the loop are reversed. This would push the loop back in the other direction, preventing it from rotating, and making it oscillate back and forth instead.

21
Q

Why would you not use a battery in a transformer?

A

Batteries provide a DC current, which won’t work in a transformer.

22
Q

Why does a transformer need an AC current?

A

To create an induced current in the secondary coil there must be changing flux through the coil. Only produced by an alternating current.

23
Q

What does an electric field that changes in time create?

A

A magnetic field

24
Q

What will happen if a current carrying coil is placed in a magnetic field?

A

It will cause motion.

25
Q

What happens when a coil is moved in a magnetic field?

A

It will produce a force on the charged particles (electrons) within the coil. This causes a current to flow.

26
Q

What does emf mean

A

Potential difference

27
Q

What is emf measure in?

A

Volts

28
Q

Where in the conductor is the emf induced?

A

Between the ends of the conductor.

29
Q

If there is a magnet or coil moving in a magnetic field, what would stop it from producing the emf?

A

In the conductor did not cut the field, ie it is parallel, it will not produce an emf. The magnetic field must be changing.

30
Q

What is Faraday’s law?

A

Induced EMF is directly proportional to the rate of change of magnetic flux.

31
Q

The faster that the magnetic flux through a circuit changes, the greater the ___________ that is produced.

A

EMF

32
Q

What are three ways to increase the magnetic flux through a circuit?

A

Change the velocity with which the magnet or coil moves
Change the strength of the magnetic field
Change the area of the coil

33
Q

What is Lenz’s Law?

A

An induced current always flows in such a direction as to oppose by its own magnetic field, the motion or change that induced it.

34
Q

What will happen when the magnets North Pole is moved towards the front of the coil?

A

The coil induces a current flow that opposes this movement. It creates a North Pole to repel the incoming North Pole.

35
Q

What will happen when a magnets North Pole is moved away from the front of a coil?

A

The coil will induce a current with a flow that will oppose this movement. It will create a South Pole to attract the retracting North Pole.

36
Q

Where is the emf induced when a conducting disk rotates such that it cuts a magnetic field?

A

Between its centre and its circumference.

37
Q

What is the armature?

A

A coil of wire that rotates between the poles of a magnet.

38
Q

What are the three factors that can increase the emf of a generator?

A

Increasing the speed of rotation of the armature
Increase the number of turns in the coil of the armature
Use a stronger magnetic field

39
Q

What is back emf?

A

It is the induced emf of the armature rotating in the magnetic field. This emf resists the applied emf that drives the current through the armature (Lenz law)

40
Q

What is the net emf in a motor?

A

The applied emf- the back emf.

41
Q

What is a transformer?

A

A device used to increase or decrease AC voltage.

42
Q

How does a transformer work?

A

A AC current is passed through a primary coil, producing a changing magnetic field that threads through the secondary coil. The changing magnetic field produces an emf in the secondary coil.

43
Q

What are eddy currents?

A

When a conductor moves in a changing magnetic field, electromagnetic induction can set up circulating currents in the conductor.

Physics (7 decks)

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