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physics content > Magnetic Fields > Flashcards

Magnetic Fields Flashcards

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1
Q

What is required for a magnetic field to be induced?

A

A current must flow through a wire

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2
Q

How can you identify the direction of concentric rings around a wire?

A

Through the right hand rule

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3
Q

What is magnetic flux density?

A

It is a measure for the strength of a field

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4
Q

What happens when a field is perpendicular to the current of a wire

A

A force is exerted onto a wire

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5
Q

What does each finger represent in flemings left hand rule?

A

Thumb = motion of the force
first finger = direction of field
second finger = direction of conventional current (opposite to electron flow)

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6
Q

What is the direction of a field

A

It is from north to south

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7
Q

Why do particles follow a circular path in a magnetic field

A

Force exerted is always perpendicular to the direction of motion, as the force induced acts as a centripetal force

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8
Q

Where can you find the application of charged particles in a magnetic field

A

In a particle accelerator called a cyclotron

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9
Q

List the characteristics of a cyclotron:

A
  • made up of two dees
  • has a uniform field perpendicular to the plane of electrodes
  • has high alternating voltage
  • the particles speed does not increase due the magnetic field
  • the particles speed is accelerated by the electric field when crossing the gap
  • when the particle reaches the gap again the AC changes to allow acceleration again
  • the radius increases every time
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10
Q

What is magnetic flux

A

The value which describes the magnetic field or magnetic field lines passing though a given area, when the field is perpendicular to an area

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11
Q

What is magnetic flux linkage?

A

Magnetic flux multiplied by the number of turns (N)

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12
Q

What happens when a current is not perpendicular to the magnetic field

A

There is components of magnetic flux found in the perpendicular components of the current found by using trigonometry

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13
Q

What is electromagnetic induction?

A

This is when conducting rods move relative to a magnetic field, the electrons in the rod will experience a force and build up to one side of a rod causing an emf to be induced

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14
Q

What are the two laws that govern the effects of electromagnetic induction?

A

Faraday’s law - magnitude to induce emf is equal to rate of change of flux linkage
Lenz’s law - direction of induced current is such as to oppose the motion causing it

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15
Q

What is the peak to peak value of voltage in the UK’s power line

A

650V

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16
Q

What is the UK’s RMS voltage

A

230

17
Q

How do you calculate RMS voltage

A

peak volatge / root 2 (325/root 2) = 230V

18
Q

what is the mean voltage of UK power

A

0 because alternating current goes negative and positive

19
Q

How is an eddy current occur in a transformer

A

When magnetic field changes
- emf in the core is induced
- this causes current to flow in the core

20
Q

How can you reduce loss due to eddy current

A

By laminating the core

21
Q

How do you reduce loss in a transformer?

A
  • using thicker wires
  • using an easily magnetised core
  • laminating the core
22
Q

How does acceleration impact the path of a proton in a cyclotron

A

Proton spirals outwards

  • as velocity increases the radius increases
23
Q

What electromagnetic radiation has the same wavelength of a proton

A

gamma rays

24
Q

Define magnetic flux density

A

It is the flux density that produces a force of 1N per 1m of wire when current is 1A

25
Q

How does a transformer induce emf?

A

When the AC changes the magnetic field,
this induces emf use to rate of change of flux linkage

26
Q

What would happen in a velocity selector if the ion emitted had a slower speed than normal?

A

slower ions would be deflected more

27
Q

If two coils are next to each other and an emf is induced due to the first coil onto the second coil, how long will this emf last

A

Momentarily

28
Q

If flux is decreased what happens?

A

An emf is induced to oppose magnetic flux, leading to a current on the opposite direction

29
Q

What properties of a magnet, coil and spring needed to make a geo phone sensitive?

A

Strong magnetic field
many coil turns
low spring constant springs
large mass magnet
low resistance coil

30
Q

explain the function of the core

A

Provides greater linkage

31
Q

Explain function of secondary coil

A

It is a conductor with varying magnetic flux
Produce an emf determined by the number of turns

32
Q

Explain the function of a laminated core?

A

laminated core made from highly resistive materials,
this reduces eddy current

thin sheets of iron is used, so smaller emf are induced in the core

physics content (19 decks)

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