Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

AQA A Level Physics(Option A: Astrophysics) > Magnetic Fields > Flashcards

Magnetic Fields Flashcards

You may prefer our related Brainscape-certified flashcards:
Physics 101 flashcards AP® Physics flashcards
1
Q

What is a magnetic field?

A

A region in which a force will act on magnetic materials or induced magnets

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What are field lines?

A
  • A way of representing a force field
  • Called flux lines in a magnetic field
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Which way do field lines travel for bar magnets?

A

From north to south

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Describe the diagram for two north magnets facing each other

A
  • Lines curving away from each other
  • Arrows pointing outward
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What happens when a current flows through a wire?

A
  • A magnetic field is induced around the wire
  • The field lines are concentric circles centred around the wire
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

How is the direction of the magnetic field induced by a wire identified?

A

By using the right hand rule

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What happens when a current carrying wire is put into a external magnetic field?

A
  • The field from the wire and magnets combine, causing a resultant field.
  • Where the field is stronger, the lines are closer together
  • These bunched up lines cause a resulting force on the wire, perpendicular to the direction of the magnetic field
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

How is the direction of the force identified?

A
  • Fleming’s left hand rule
  • Upward: Force
  • Forward: External magnetic field
  • Right: Current (Positive to negative)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Define magnetic flux density

A

The force on one metre of wire carrying a current of one amp, perpendicular to the magnetic field

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Derive the equation for the circular path of particles

A
  • F = mv²/r = BQv
  • mv²/r = BQv
  • mv = BQr
  • r = mv/BQ
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

State the equation, which includes v, for the frequency of an object in circular motion

A

f = v/2πr

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Derive State the equation for frequency of rotation in terms of B, Q and m.

A
  • f = v/2πr and r = mv/BQ
  • f = v/2π(mv/BQ)
  • f = 1/2π(m/BQ)
  • f = BQ/2πm
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

State one application of circular motion of particles

A

Particle accelerators, i.e cyclotrons

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Describe how a cyclotron works

A
  • Charged particles are produced and fired into one of the two hollow semicircle electrodes with a uniform magnetic field
  • The uniform magnetic field is applied perpendicular to the plane of the electrodes which have an alternating p.d between them
  • Charged particles are accelerated in a circular path by an applied p.d in the electrodes
  • As particles speeds up, path radius is bigger until it exits the cyclotron at high speed
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Define magnetic flux

A

The number of field lines passing through an area, in Webers

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

How is an electromotive force induced?

A

When there’s relative motion between a conducting rod and a magnetic field

17
Q

Define electromotive force

A
  • Energy transferred from chemical energy to electrical energy in a power supply
  • Electrical energy per unit charge
18
Q

State Faraday’s Law

A

Induced e.m.f is directly proportional to rate of change of flux linkage

19
Q

State Lenz’s Law

A

The induced e.m.f is always in such a direction as to oppose the change that caused it

20
Q

What do generators do?

A
  • Convert kinetic energy into electric energy
  • They induce an electric current by rotating a coil in a magnetic field
21
Q

State the equation for average power

A

Average power = I(rms) x V(rms)

22
Q

What is the value for UK mains electric supply?

A

230V(rms)

23
Q

What is a transformer?

A

Devices which make use of electromagnetic induction to change the size of the voltage for an alternating current

24
Q

Describe how a transformer works

A
  • An alternating current flowing in the primary coil causes the core to magnetise, demagnetise and re-magnetise continuously in opposite directions
  • This produces a rapidly changing magnetic flux across the core which is why a magnetically soft material is needed(iron or special alloy)
  • Rapidly changing flux in iron core passes through secondary coil
  • This induces an alternating voltage of the same frequency
25
Q

State the 2 types of transformers and their roles

A
  • Step up transformers: Increase the voltage by having more turns on the secondary coil than primary coil
  • Step down transformers: Decrease the voltage by having more turns on the primary coil than secondary coil
26
Q

State the factors which cause a transformer to have a decrease in efficiency

A
  • Eddy currents
  • Heat by resistance in the coils
  • Heat by magnetising and demagnetising the core
  • Magnetic flux loss over distance
27
Q

What are eddy currents?

A

Looping currents induced by the changing magnetic flux in the core

28
Q

How do eddy currents decrease efficiency in a transformer?

A
  • The rapidly changing flux cuts the metallic core, inducing an e.m.f
  • This e.m.f induces looping currents in the core
  • The currents create a magnetic field which opposes the field which induced them, reducing field strength
  • They also dissipate energy by generating heat
29
Q

How can a transformer be adapted to reduce the effect of eddy currents?

A

By having layers of the core separated out by a thin insulator, so a current can’t flow (laminating the core)

30
Q

How can a transformer be adapted to reduce energy lost by heat as resistance in the coils?

A

Use wires with low resistance, such as thick copper wire which has a low resistivity and a larger diameter meaning smaller resistance

31
Q

How can a transformer be adapted to reduce the energy lost as heat by magnetising and demagnetise the core?

A

By using a magnetically soft material which magnetises and demagnetises easily, such as iron

32
Q

How can a transformer be adapted to reduce the magnetic loss from the primary coil to the secondary coil?

A

By designing the core so that the coils are as close as possible

33
Q

For the national grid, state the equation for the power losses due to resistance of the cables

A

P = I²R

34
Q

Define Terminal Potential Difference

A
  • Energy transferred from electrical energy to another type
  • Work done per unit charge

AQA A Level Physics(Option A: Astrophysics) (15 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions