Brainscape's Knowledge GenomeTM

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


See full index

Physics > Magnetic Fields > Flashcards

Magnetic Fields Flashcards

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

Define a Magnetic Field

A

A field surrounding a permanent magnet or a current-carrying conductor in which magnetic objects experience a force

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

Describe Magnetic Field lines

A

Arrows point from north to south
Equally spaced and parallel magnetic field lines represent a uniform field - strength of the magnetic field does not vary
Field is stronger when the magnetic field lines are closer
Like poles repel and unlike poles attract

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

What happens when a wire carries a current

A

A magnetic field is created around the wire, the field is created by the electrons moving within the wire.

Any charged particle that moves creates a magnetic field in the space around it

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

What are magnetic field lines for a current-carrying wire

A

Concentric circles centred on the wire and perpendicular to it - right hand grip rule can be used to determine the direction of magnetic field

Thumb points in the direction of the conventional current

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

Magnetic field lines in a coil

A

North and south poles at the opposite faces

Refer to text book to check descriptions

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

What is the strength of magnets and magnetic fields measured in

A

Tesla (T)

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

What happens when a current-carrying conductor is placed in an external magnetic field

A

Two fields interact just like the fields of two permanent magnets, they experience equal and opposite forces

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

What happens when a current-carrying wire is placed between the poles of a magnet

A

The direction of the force experienced by a current-carrying conductor placed perpendicular to the external magnetic field can be determined using Fleming’s Left Hand rule

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

Flemings Left Hand Rule

A

Fuck - Force
Man - Magnetic Field
City - Current

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

What is the magnitude of the force experienced by a wire in an external magnetic field dependent on

A

Force is directly proportional to current, length, sin theta and strength of the magnetic field

F = BILsin(theta)

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

What is Magnetic Flux Density

A

Strength of a magnetic field
Measured in Tesla

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

Is magnetic flux density a vector or scalar

A

Vector

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

Motion of a charged particle in a magnetic field

A

Circular

Straight line once out of the field

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

Why does a current-carrying wire experience a force in a magnetic field

A

Each electron in the wire experiences a tiny force

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

What is the force on a charged particle in a magnetic field

A

Perpendicular to its velocity, therefore, has no effect on velocity

F = BQV

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

What can = force on an electron in a magnetic field

A

mv^2 / r

17
Q

What is radius of a charged particles circular path proportional to

A

velocity and mass

18
Q

What is radius of a charged particles circular path inversely proportional to

A

Magnetic fields, charge

19
Q

How to induce an emf

A

A coil, magnet and sensitive voltmeter are needed.

Attach the voltmeter to a coil.

When the magnet is pushed towards the coil, an emf is induced across the ends of the coil

When the magnet is pulled away, a reverse emf is induced.

Repeatedly pushing and pulling will induce an alternating current.

Faster the magnet is moved, the larger the induced emf.

20
Q

Explain EM Induction

A

Energy is always conserved.

Some of the work done to move the magnet is transferred into electrical energy. The motion of the coil relative to the magnetic field makes the electrons move because they experience a magnetic force Bqv.

The moving electrons constitute an electrical current within the coil, so the process has produced electrical energy

21
Q

Define Magnetic Flux

A

Product of the component of the magnetic flux density perpendicular to the area and the cross-sectional area

Magnetic Flux = BAcos(theta)

Units = Wb

22
Q

What is Magnetic Flux linkage

A

Product of the number of turns in the coil and the magnetic flux

23
Q

When is an emf induced in a circuit

A

When there is a change in the magnetic flux linking the circuit

24
Q

What is Faradays Law

A

Magnitude of the induced emf is directly proportional to the rate of change of magnetic flux linkage

The constant of proportionality is -1

25
Q

What happens when a magnet is moved towards a coil with no voltmeter connected across it

A

If the magnet is moved towards the coil, the induced current is such that the end facing the magnet is north pole - work needs to be done in order to push the magnet towards the coil.

If the end was a south pole, then principal of conservation of energy would be violated, as the attraction between the coil and the magnet creating electrical energy out of nowhere

Work done is equal to the electrical energy produced in the coil

26
Q

What happens when a magnet is moved away from a coil with no voltmeter connected across it

A

The motion of the magnet must once again be opposed so that you do work. The end the magnet is moving away from becomes the south pole

27
Q

What is Lenz’s Law

A

Direction of the induced emf or current is always such as to oppose the change producing it

28
Q

What is Lenz’s Law

A

The direction of the induced emf or current is always such as to oppose the change producing it

29
Q

Explain how an AC generator works using Faraday’s Laws

A

Has a flux linkage
As the coil rotates at a steady frequency, the flux linkage changes with time t. This variation is sinusoidal and is caused by the changing cos(theta)

For a given generator, induced emf is directly proportional to rate of change in cos(theta)

30
Q

What does a simple transformer consist of

A

A laminated iron core, a primary (input) coil and a secondary (output) coil

31
Q

How do transformers work

A

An alternating current is supplied to the primary could
This produces a varying magnetic flux in the soft iron core
The secondary coil is linked by this changing flux
The iron core ensures that all the magnetic flux created by the primary coil links the secondary could and none is lost
A varying emf is produced across the ends of the secondary coil

32
Q

Describe a step-up transformer

A

Has more turns on the secondary than on the primary coil

33
Q

Describe a step-down transformer

A

Fewer turns on the secondary coil than on the primary coil

34
Q

How can transformers be made efficient

A

Low-resistance windings help reduce power losses due to the heating effect of the current

Making a laminated core with layers of iron separated by an insulator helps to minimise currents induced in the core itself (eddy currents) - minimises loss due to heating

35
Q

What is a velocity selector

A

Device that uses both electric and magnetic fields to select charged particles of specific velocity

Two parallel horizontal plates connected to a power supply produce a uniform electric field of field strength E between the plates.

A uniform magnetic field of flux density B is also applied perpendicular to the electric field.

Charged particles travelling at different speeds that are to be sorted enter through a narrow slit Y.

Electric and Magnetic Field Lines deflect them in opposite directions - only for particles with a specific speed v will these deflections cancel so that they travel in a straight line and emerge from a narrow slit Z

For an undeflected particle - Electric force = Magnetic force

EQ = BQv

v = E / B

Physics (19 decks)

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