Magnetic Fields Flashcards

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

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
How does a transformer induce emf?
When the AC changes the magnetic field, this induces emf use to rate of change of flux linkage
26
What would happen in a velocity selector if the ion emitted had a slower speed than normal?
slower ions would be deflected more
27
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
Momentarily
28
If flux is decreased what happens?
An emf is induced to oppose magnetic flux, leading to a current on the opposite direction
29
What properties of a magnet, coil and spring needed to make a geo phone sensitive?
Strong magnetic field many coil turns low spring constant springs large mass magnet low resistance coil
30
explain the function of the core
Provides greater linkage
31
Explain function of secondary coil
It is a conductor with varying magnetic flux Produce an emf determined by the number of turns
32
Explain the function of a laminated core?
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