Brainscape's Knowledge GenomeTM

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


See full index

Physics A2 > Magnetic Fields > Flashcards

Magnetic Fields Flashcards

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

Describe and explain what happens when a current carrying wire is entered into an external magnetic field

Which hand rule can be used to describe the components involved?

A

A current carrying wire is entered into an external magnetic field
Field of wire and magnetic field are added to produce a resultant force
Magnetic field lines are perpendicular to the direction of current

LHF

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

At what angle does a current carrying wire experience the greatest resultant force?

A

90 degrees

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

Define magnetic flux density

Unit? (2 possibilities)

Is it a scalar or vector quantity?

A

The force per unit length per unit current on a current carrying at right angles to the magnetic field lines

T or Nm-1A-1

Vector

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

What does F represent in the equation F=BIL

A

The maximum force that a current carrying wire experiences in an external magnetic field - when it is at 90 degrees to the field

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

Describe right hand rule

When are these two components switched?

A

Fingers represent direction of magnetic field
Thumb is direction of current of current carrying wire

When describing a wire coil

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Describe left hand rule

What else can the thumb represent? When does the thumb represent this component?

A

First finger field
Second finger current
Thumb is movement of a current carrying through an external mag field

Direction of resistive force which is opposite to motion due to external force
When emf is induced, when lenz law is applicable, when external force is acting

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

What is the direction of current relative to an electron moving though a magnetic field?

A

Current is in opposite direction to direction of electron

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What happens if an electron leaves a magnetic field?

What happens if it doesn’t? Why?

A

It travels in a straight line

Circular motion will occur because the direction of force is at right angles to the direction of the electrons movement. (Centripetal force)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Describe and explain the cyclotron

4 points

A

Magnetic field forces particle into and out of electrode via a semi circular path
Alternating p.d accelerates particle into opposite electrode
V increases so r increases and the direction of p.d switches, causing process to continue
Particle leaves cyclotron as a beam

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

Define total magnetic flux

Unit?

A

Total magnetic flux density in a given area of an object

Webers, Wb

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Define flux linkage

Unit?

A

The size of emf induced when a wire coil is moved through a magnetic field or vice versa

Wb

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

What is Faraday’s law?

A

Induced emf is directly proportional to the rate of change of flux linkage

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is the gradient of a Flux linkage against time graph?

A

Emf

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

What is the area of an induced emf against time graph?

A

Flux linkage

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is Lenz’s law?

A

The induced emf is always in such a direction as to oppose the change that caused it

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

Describe how the opposing force to movement is generated, when a wire coil is moved through a magnetic field

A

Object moves right with velocity due to an external force
It cuts field lines, generating eddy currents
Current produces an opposing field which causes an opposing field to movement

17
Q

When lenz’s law applies, what does the thumb represent in the LHF rule?

I’m which direction is the motion of the conductor?

A

Direction of force of resistance

Opposite

18
Q

How does flux linkage and emf vary when a coil rotates uniformly in a magnetic field?

A

Sinusoidally

19
Q

What is the phase difference between flux linkage and emf when there is a rotating wire coil?

A

They are 90 degrees out of phase

20
Q

When and at what angles is flux linkage greatest?

When and at what angles is emf greatest?

A

At 0 and 180 degrees - coil is perp

At 90 and 270 degrees - coil is parallel

21
Q

How does a generator work?

What is another name for a generator?

A

Converts kinetic energy to electrical energy by inducing an alternating current from a rotating coil in a magnetic field

Dynamo

22
Q

What happens if the number of turns in a transformer doubles?

A

The voltage doubles

23
Q

What are the reasons for energy loss in a transformer? What are their solutions?

(3)

A

Heating of coils - using low resistance windings

Generated eddy currents heat core - use laminated core

Constantly changing magnetic field - use a soft iron core because it magnetizes and demagnetizes easily

24
Q

What is the relative number of coils on a step up transformer?

A

No of coils on secondary coil is greater then number of coils on primary coil

25
Q

Why do we step up voltage?

A

To decrease current so that heat loss is minimized

26
Q

How does a transformer work?

5 points

A

Alternating current flows through primary coil
This causes the core to magnetise and demagnetise continuously in opposite directions
Rapidly changing magnetic flux is produced across core
Rapidly changing magnetic flux passes through secondary coil
This induces an alternating voltage of the same frequency but a different voltage (assuming no of coils is different)

27
Q

How does current vary with an AC power supply

A

Sinusodially

28
Q

What does “same load “ mean?

A

Under the same resistance

29
Q

What is the relation between the Irms value of an AC and the I value of a DC?

A

Irms has the equivalent heating affect as direct current with the same value

30
Q

How can you use an oscilloscope as a voltmeter to find:

  1. Vrms
  2. Frequency
A

Connect power supply to INPUT of the oscilloscope
Switch time base setting OFF and adjust y gain until a complete vertical line is seen
Measure length of the line and convert it to peak to peak voltage WITH CALIBRATION
(For D.C, measure just the peak voltage)
Divide by root 2 to get Vrms

Switch time base setting ON, adjust it until a minimum of 1 cycle is seen on screen
Measure length of one cycle and convert it to time period using time base setting
F = 1/T

31
Q

Does an electron undergo circular motion when perpendicular to an electric field?

A

No. Just parabolic motion

32
Q

What happens to the motion of an electron due north is inserted into a magnetic field due south

A

It will continue moving north with constant velocity

33
Q

What happens when a wire with alternating current passes through a magnetic field? Why?

A

It will vibrate vertically because the force is perpendicular to Magnetic flux density and current
Force acts in opposite direction when current reverses
Continual reversal means process is repeated

Physics A2 (11 decks)

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