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A Level Physics > Magnetic Fields > Flashcards

Magnetic Fields Flashcards

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1
Q

What does a current-carrying conductor produce

A

a magnetic field

When interacting with an external magnetic field, it will experience a force

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2
Q

When will a current-carrying conductor experience the maximum magnetic force

A

if the current through it is perpendicular to the direction of the magnetic field lines

It experiences no force if it is parallel to magnetic field lines

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3
Q

What is the strength of the magnetic field known as, and what is its unit

A

the magnetic flux density, B

measured in Tesla (T)

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4
Q

Describe the components of the force-flux density equation

A
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5
Q

What does the force-flux density equation show

A

the greater the current or the magnetic field strength, the greater the force on the conductor

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6
Q

What is Flemings’s left hand rule

A
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7
Q

What are the symbols for a magnetic field which goes into or out of the page

A
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8
Q

Describe how moving charges may curve in direction

A

For example, when a positively charged particle enters a magnetic field into the page from left to right:

-Using Fleming’s left-hand rule, the first finger points into the page and the second finger (current) points to the right
- This means the force is upwards
- The particle is then pulled in the direction of this force (upwards). This means the direction of the current also changes direction slightly (slanting upwards)
- This means the force will also change direction since it still needs to keep perpendicular to the current and the field
- Therefore, the moving charges will follow a circular trajectory

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9
Q

Magnetic flux density def

A

The force acting per unit current per unit length on a current-carrying conductor placed perpendicular to the magnetic field

Measured in Tesla

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10
Q

unit of a Tesla def

A

A wire carrying a current of 1A normal to a magnetic field of flux density of 1 T with force per unit length of the conductor of 1 N m-1

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11
Q

how can a particle experience no magnetic force

A

when it travels parallel to a magnetic field

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12
Q

What does the force on a current carrying wire depend on

A
  • Strength of uniform magnetic field
  • Size of current
  • Length of wire in the field
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13
Q

For a particle in a magnetic field, travelling in a circular path, what is the centripetal force

A

The magnetic force

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14
Q

Draw a diagram of the forces acting on a particle which moves in a circular path

A
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15
Q

What are cyclotrons

A

a type of particle accelerator that accelerates charged particles (eg. protons) from their centre along a spiral path

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16
Q

What kind of medical research are cyclotrons used for

A

Producing medical isotopes (tracers)

Creating high-energy beams of radiation for radiotherapy

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17
Q

Draw and label a diagram of a cyclotron

A
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18
Q

Describe the process of accelerating a particle in a cyclotron

A
  • A source of charged particles is placed at the centre of the cyclotron and they are fired into one of the electrodes
  • The magnetic field in the electrode makes them follow a semi-circular path, since it is perpendicular to their motion until they eventually leave the electrode
  • The potential difference applied between the electrode accelerates the particles across the gap to the next electrode (since there is an electric field in the gap)
  • Since the speed of the particles is now higher, they will follow a circular path with a larger radius (since r ∝ v) before leaving the electrode again
  • The potential difference is then reversed so the particles accelerate towards the opposite electrode
  • This process is repeated as the particles spiral outwards and eventually have a speed large enough to exit the cyclotron
  • The alternating potential difference is needed to accelerate the particles across the gap between opposite electrodes
  • Otherwise, the particles will only accelerate in one direction
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19
Q

Derive the equation for the radius of the path of a particle travelling in a magnetic field

A
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20
Q

What is electromagnetic induction and give examples

A
  • when an e.m.f is induced in a closed circuit conductor due to it moving through a magnetic field
  • This happens when a conductor cuts through magnetic field lines
  • The amount of e.m.f induced is determined by the magnetic flux

Examples are a flat coil or a solenoid

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21
Q

magnetic flux definition

A

The product of the magnetic flux density and the cross-sectional area perpendicular to the direction of the magnetic flux density

(the total magnetic field that passes through a given area)

22
Q

When is magnetic flux at a maximum/minimum

A
  • It is a maximum when the magnetic field lines are perpendicular to the plane of the area
  • It is 0 when the magnetic field lines are parallel to the plane of the area
23
Q

Draw a diagram of maximum magnetic flux and minimum magnetic flux

A
24
Q

What is the unit of magnetic flux

A

Webers (Wb)

25
Q

What do the components of the magnetic flux equation mean

A
26
Q

Magnetic flux linkage def

A

The product of the magnetic flux and the number of turns of the coil

27
Q

What do the components of the magnetic flux linkage equation mean

A
28
Q

What is magnetic flux linkage measured in

A

Weber turns (Wb turns)

29
Q

What is the symbol for magnetic flux linkage

A

ΦN

30
Q

What do the components of the magnetic flux linkage equation mean (When the magnet field lines are not completely perpendicular to the area A)

A
31
Q

When is an emf induced in a circuit

A

When there is:
- A changing magnetic flux density B
- A changing cross-sectional area A
- A change in angle θ

32
Q

What is electromagnetic induction

A

when an e.m.f is induced when a conductor moves through a magnetic field

33
Q

What happens when a conductor cuts through magnetic field lines

A
  • This causes a change in magnetic flux (ΔΦ)
  • Which causes work to be done
  • This work is then transformed into electrical energy
34
Q

Electromagnetic induction def

A

The process in which an e.m.f is induced in a closed circuit due to changes in magnetic flux

35
Q

When may electromagnetic induction occur

A

When:
- A conductor cuts through a magnetic field
- The direction of a magnetic field through a coil changes

36
Q

What is electromagnetic induction used for

A
  • Electrical generators which convert mechanical energy to electrical energy
  • Transformers which are used in electrical power transmission
37
Q

What factors increase an induced e.m.f when a bar magnet is moved through a coil connected to a voltmeter to induce an e.m.f

A
  • Moving the magnet faster through the coil
  • Adding more turns to the coil
  • Increasing the strength of the bar magnet
38
Q

What factors increase an induced e.m.f when a wire is moved between two magnets connected to a voltmeter to induce an e.m.f

A
  • Increasing the length of the wire
  • Moving the wire between the magnets faster
  • Increasing the strength of the magnets
39
Q

What does Faraday’s law state

A

The magnitude of the induced e.m.f is directly proportional to the rate of change in magnetic flux linkage

40
Q

What does Lenz’s law state

A

The direction of the induced emf is such that it will oppose the change of flux producing it

41
Q

Describe the experimental evidence for Lenz’s law

A
42
Q

What do the components of Faraday’s law equation mean

A
43
Q

What does Faraday’s law equation demonstrate

A

that the gradient of a magnetic flux against time graph is the e.m.f

44
Q

What is the equation that combines Faraday and Lenz’s laws AND what does it demonstrate

A
45
Q

Draw a diagram which shows how a straight conducting rod moving through a magnetic field will have an e.m.f induced in it

A
46
Q

Derive the equation for the induced e.m.f in a conductor as it moves through the magnetic field

A
47
Q

When is induced emf at a maximum/ minimum

A
  • Maximum when θ = 90o. The magnetic field lines are parallel to the plane of the area (or the normal to the area is perpendicular to the field lines)
  • 0 when θ = 0o. The magnetic fields lines are perpendicular to the plane of the area (or the normal to the area is parallel to the field lines)
48
Q

Draw a graph of the magnetic flux linkage and e.m.f induced as a coil rotates in a magnetic field

A
49
Q

Describe the derivation and components of the ‘emf induced in a rotating coil’ equation

A
50
Q

Derive the frequency equation

A
51
Q
A
52
Q
A

A Level Physics (33 decks)

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