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A2 Physics > Magnetic field > Flashcards

Magnetic field Flashcards

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1
Q

What three things create magnetic fields around them?

A

Permanent magnets, current carrying conductors(electromagnets) and moving charged particles.

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2
Q

How can we visualise the magnetic field?

A

we can visualise the magnetic field by sketching magnetic field lines

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3
Q

which direction does a magnet point to?

A

from north to south

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4
Q

How can you work out the direction of magnetic field?

A

Fleming’s left hand rule

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5
Q

what three things can be worked out from the fleming’s left hand rule?

A

the direction of force,F,

the direction of magnetic field,B,

the direction of electric current,I

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6
Q

can you draw the magnetic field of a bar magnet?

A
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7
Q

can you draw the magnetic field of two north pole bar magnets?

A
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8
Q

can you draw the magnetic field of a north pole magenet and a south pole magnet?

A
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9
Q

what quantity would magnetic fields be

A

vector

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10
Q

what kind of loop do magnetic field lines form?

A

close loops

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11
Q

would the field lines cross each other?

A

No, the field lines never cross each other

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12
Q

________ are often used for electromagnets and why?

A

iron cores because they concentrate the magnetic field lines, and create a stronger magnetic field

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13
Q

How can we know how strong a magnetic field is?

A

it can be visualised by the dendity of the field lines - the closer they are the stronger the field

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14
Q

what is the other name and unit for magnetic field lines?

A

magnetic flux, Φm, nd is measured in webers, Wb

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15
Q

what is the other name and unit for the strength of the magnetic field?

A

magnetic flux density, B

Tesla, T

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16
Q

How do we calculate magnetic flux density? (equation)

A

B = Φm/A

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17
Q

what do wires create when currents flow through it?

A

magnetic field

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18
Q

How do we work out the direction of the field?

A

using right hand grip rule

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19
Q

what is thumb represent in right hand grip rule?

A

the direction of the current

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20
Q

can you draw the magnetic field when a current flows through a wire from (bottom is negative)

A
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21
Q

What three things create magnetic fields around them?

A

Permanent magnets, current carrying conductors(electromagnets) and moving charged particles.

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22
Q

What is a field?

A

It’s a region in which a force act

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23
Q

when _____ flow in a ______, ________is induced around the ________.

A

when current flows in a wire, a magnetic field is induced around the wire.

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24
Q

how do you work out the direction of magnetic field around a current-carrying wire?

A

right-hand rule.

25
Q

what is the thumb represent in right hand rule?

A

the direction of current

26
Q

what are the curled fingers represent in right-hand rule?

A

the direction of magnetic field

27
Q

what is a solenoid?

A

a thing with a lot of coils

28
Q

can u draw the magnetic field created by a current-carrying wire in a coil?

A

…

29
Q

can you draw the magnetic field created by a current-carrying wire in a lots of coils.

A

…. kind of like a bar magnetic

30
Q

what is motor effect?

A

the force is perpendicular to the wire and to the lines of force.

31
Q

can you draw out the motor effect?

A
32
Q

what does the magnitude of the force depends on? (5)

A

the current, the strength of the magnetic field, the length of the wire and the angle between the lines of force and the field and the current direction

33
Q

what is the eqaution for force?

A

F = BIL

34
Q

how does a motor work?

A

http://www.animations.physics.unsw.edu.au/jw/electricmotors.html

35
Q

how do you work out the velocity of a charged particle in a magnetic field?

A

V = F/BQ

36
Q

how do we find out the force which is acting on a charged particle in a magnetic field which is a x angle to the the lines of force?

A

F = Bqv sin x

37
Q

How can you make a current carring wire ina magnetic field vibrate? can you use left hand rule to find the direction of the force?

A

by passing an alternating current. (see p.73)

38
Q

what is magnetic flux density?

A

the force on one metre of wire carrying a current of one amp at right angle to the magnetic field

39
Q

what is the definition of one tesla?

A

1 tesla = 1 Wb/m2

40
Q

how do you find out the force on a current carrying wire?

A

F = Bil

41
Q

what would a charged particle experience in a magnetic field?

A

a force

42
Q

why are charged particles in a magnetic field deflected in a circular path?

A

the force is always perpendicular to the current. that’s the condition for circular motion.

43
Q

what is a particle’s acceleration?

A

a = v2/r

44
Q

how do you derive the formula for radius of the circular path?

A

F = mv2/r = BQv

mv2/r = BQv

r = mv/BQ

45
Q

how do you find out the frequency of rotation?

A

f = v/2(3.14)r

f = BQ/2(3.14)m

46
Q

what does the formular of frequency tell you?

A

the frequency of rotation of a charged particle in a magnetic field is independant of its velocity. the time it takes a particle to complete a full circle depends only on the magnetic flux density and its mass and charge

47
Q

what would happen if you increase a particle’s velocity?

A

it will make it follow a circular path with a larger radius, but it will take the same amount of time to complete it.

48
Q

If a ___________ moves through a _________ its _______ will experience a _______.

A

if a conducting rod moved through a magnetic field its electrons will experience a force.

49
Q

how to induce an emf?

A

when there is realtive motion between a conductor and a magnet

50
Q

if a conducting rod moves through a ____________ its electrons will experience a force, which means that they _______________ at ______. this induces an _______ across the ends of the rod.

A

magnetic field, accumulate, one end, emf

51
Q

flux linking

A

when an emf. is induced by changing the magnitude or direction of the magnetic flux (eg. by using an alternarting current)

52
Q

magnetic flux

A

magnetic flux density, B, is a measure of the strength of the magbetic field per unit area.

Wb = BA

53
Q

flux linkage

A

when a wire coil is moved in a magnetic field, an e.m.f. is induced across the coil.

= N Φ = BAN

54
Q

Φ = ?

A

BAcosx

BA

55
Q

what is the angle which we consider in flux linkage

A

angle between the normal to the plane of the coil and the magnetic field

56
Q

faraday’s law

A

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

magnitude of induced emf = rate of change of flux linkage

= N change of Φ / change of t

57
Q

Lenz’s law

A

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

the idea that an induced emf will oppose the change that caused it agrees with the principle of the conservation of energy

58
Q

NΦ = ?

A

BANcoswt

theta = wt

59
Q
A

A2 Physics (8 decks)

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