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Physics > Magnetism And Electromagnetisms > Flashcards

Magnetism And Electromagnetisms Flashcards

1
Q

Which way does the magnetic field point?

A

From the north to the south

In through the south and out through the North

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2
Q

Do field lines ever cross eachother?

A

Never

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3
Q

What do compass needles do when near field lines?

A

Compass needles always lie along field lines.

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4
Q

Define a magnetic field.

A

An area where magnetic material would feel a force.

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5
Q

What do the poles on a magnet do?

A

Always seek the direction of the poles they represent.

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6
Q

Like poles……

A

Repel.

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7
Q

Unlike poles…

A

Attract.

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8
Q

What materials attract to a magnet?

A

Iron, steel, nickel and cobalt.

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9
Q

What materials do not attract to a magnet?

A

Lead. Gold, plastic, glass.

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10
Q

What is the difference between magnetically hard and magnetically soft materials? Give examples.

A

Magnetically soft materials: easy to magnetise, but lose magnetic properties quickly, e.g. SOFT iron.

Magnetically hard materials: remain magnetised long after being magnetised, become permanent magnets, e.g. HARD steel.

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11
Q

What is a uniform magnetic field and how can you create one?

A

Magnetic field lines that are the same distance apart and are travelling in the same direction with the same field strength everywhere.

To create one, place two flat magnets parallel to each other, with the opposite poles facing.

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12
Q

What is produced when current flows through a wire?

A

A magnetic field around it.

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13
Q

How can you tell which way the magnetic field lines are travelling through a wire.

A

Right hand grip rule.

Make a thumbs up or down, depending on the direction of the current through the piece of wire (thumb must follow the current) once your thumb has found this, the direction your four fingers are facing is the direction the magnetic field lines are travelling in (either clockwise or anti-clockwise).

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14
Q

What shape are magnetic field lines?

A

Circular.

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15
Q

What is the real current?

A

The fact that electrons actually flow from - to +.

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16
Q

What is the ‘conventional’ current?

A

The assumed, and commonly used current, that electrons flow from + to -.

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17
Q

What is a solenoid?

A

A long coil.

18
Q

What would happen to a magnetic field if you used a larger current, used more coil or added an iron core?

A

The strength of the magnetic field would increase.

19
Q

What happens to an electromagnet when you switch off the current?

A

It looses its magnetism.

20
Q

What are the symbols and units for each of the following

a) current
b) voltage
c) power?

A

a) current, I, measured in amps, A.
b) voltage, V, measured in volts, V.
c) power, P, measured in watts, W.

21
Q

Define a magnetic field line.

A

A magnetic field line shows the direction of force of the magnetic field.

22
Q

Describe an experiment to investigate the magnetic field pattern for a permanent bar magnet and that between two bar magnets.

A
  • place bar magnet or magnets under a piece of paper.
  • sprinkle iron filings on top of the paper over the bar magnet(s).
  • tap the paper to guide the iron filings.
  • record the magnetic field pattern.
23
Q

Describe the construction of electromagnetic induction (Dynamo effect).

A
  • connect an ammeter to a conduct
  • move the conductor through a magnetic field
  • the ammeter will show the magnitude and direction of the induced current.
  • if direction of movement is reversed, then the induced voltage or currents is also reversed.
24
Q

What will magnetic field lines around a straight wire look like?

A

Depending on direction if current, field lines will make simple circles around straight wire, either travelling clockwise or anti-clockwise (can be figured out using right hand grip rule).

25
Q

What will magnetic a flat circular could look like?

A

Imagine a circle shape of coil, like a ring, magnetic field lines will travel straight through the centre of the ring of coil, travelling from north to South, and they will also make flat circle shapes around each side of wire on the circular coil (see page 64 CGP).

26
Q

What will magnetic field lines around a solenoid look like?

A

The same as magnetic field lines around a bar magnet look like. Travelling from North to South, in through the south and out through the North.

27
Q

What happens to a charged particle when it moves through a magnetic field?

A

It experiences a force.

28
Q

What happens when a current carrying wire in a magnetic field?

A

It will experience a force.

Direction of force: use Fleming left hand rule.

  • first finger (index) = direction of field lines.
  • second finger (middle) = direction of current.
  • so thumb shows direction of force.
29
Q

How is the fact that a current carrying wire will experience a force in magnetic field lines applied to loudspeakers?

A
  • when a current flows the coil it creates a magnetic field.
  • magnetic field in coil either attracts or repels the permanent magnet.
  • coil moves in and out and makes diaphragm vibrate.
  • vibrations in diaphragm make air vibrate, making sound.
30
Q

How is the fact that a force is exerted on a current carrying wire in a magnetic field applied to simple d.c. electric motors?

A
  • when a current flows through the coil a magnetic field is created and the wire experiences a force.
  • force in different directions on each side of the coil makes the coil rotate.
  • commutator ensures the current always flows in same direction as the magnetic field.
  • reference to left hand rule to predict direction of force.
31
Q

How would you predict which way a wire will move when it is perpendicular through a magnetic field?

A

Using Flemings left hand rule, the direction of the force (thumb) is the same way as the direction that the wire will go in.

32
Q

How would you increase the force on a current carrying wire in a magnetic field?

A

By increasing the current or increasing the magnetic field.

33
Q

What happens if a wire is moved through a magnetic field or experiences a changing magnetic field? And how would what happens be increased?

A

A voltage is induced in the wire, as cutting field lines produces electricity.

You can increase the voltage by:

  • putting more turns on the coil
  • using stronger magnets
  • moving the wire faster
34
Q

Describe the generation of electricity by the rotation of a magnet within a coil of wire and describe the factors that affect the size of the induced voltage.

A

A dynamo is an example of the rotation of a magnet within a coil of wire generating electricity. The magnet rotates (so is moving through a magnetic field, making electricity.

More loops on coil = increased voltage
Faster speed of rotation = increased voltage.

35
Q

Describe the generation of electricity by a coil of wire within a magnetic field and describe the factors that affect the size of the induced voltage.

A

A turning coil of wire moves within a uniform magnetic field, cutting field lines and so producing electricity.

More loops on coil = increased voltage
Faster speed of rotation = increased voltage.

36
Q

Describe the structure of a transformer and how it works.

A
  • Magnetic field around the transformers soft iron core.
  • primary coil on the AC input side of the transformer has different number of turns to the secondary coil on the AC output side of the transformer.
  • ac passes through primary coil
  • this induces alternating magnetic field in coil and core
  • secondary coil experiences changing magnetic field
  • so ac and a voltage is induced in secondary coil.
  • only work on ac not dc because you need a changing magnetic field
  • soft iron core strengthens magnetic field, and is only temporarily magnetised
37
Q

What is the equation for the relationship between the primary input and the secondary output regarding the amount of voltage and number of coil turns at each?

A

Vp / Vs = Np / Ns

Primary voltage / secondary voltage = number of turns on primary coil / number of turns on secondary coil.

38
Q

What is the relationship between input power and output power?

A

Vp x Ip = Vs x Is

Primary voltage x primary current = secondary voltage x secondary current.

39
Q

Explain the use of step up and step down transformers in the large scale generation and transmission of electrical energy.

A

Step up transformers: used between power station factories and power lines as power lines need high voltage so low current, to reduce energy loss due to heating of wires.

Step down transformers: used between power lines and homes as homes need low voltage and current to decrease risk of electrocution, as voltage coming directly from power lines would fry homes.

40
Q

What is the motor effect?

A

When a current carrying wire is put in a magnetic field, there is a force on the wire and this can cause the wire to move, the motor effect.

41
Q

What is an electromagnet?

A

A material that can become temporarily magnetised when an electric current flows through it.

42
Q

What is the Dynamo effect?

A

Using electromagnetic induction to transform kinetic energy into electrical energy.

Physics (8 decks)

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