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Physics A level OCR > Magnetic fields (C23) > Flashcards

Magnetic fields (C23) Flashcards

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1
Q

What is a B field

A

A region in which a magnetic material experiences a force

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2
Q

Symbol for a magnetic field

A

B (vector)

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3
Q

Which way do field lines point

A

Direction North pole would move (N–>S)

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4
Q

What do equally spaced field lines mean

A

uniform field strength

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5
Q

Why are materials magnetic

A

Electrons have spin, giving a dipole
This can give regions (domains) a net dipole if the spin aligns
Domains with roughly aligned dipoles give a magnetic material

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6
Q

what is a soft magnetic material

A

Loses dipole after magnet is removed

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7
Q

What is a hard magnetic material

A

Domains remain aligned

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8
Q

How do current and magnetic field relate

A

RH rule

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9
Q

What does a wire into the page look like

A

Cross in circle

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10
Q

Wire out of the page

A

dot in circle

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11
Q

What is a solenoid

A

Coil with multiple turns

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12
Q

How do you work poles of a solenoid

A

Draw with dot and cross wires and look at general field

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13
Q

What does a iron core do

A

Reduces leakage, magnetic fields prefers to go through a magnetic field

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14
Q

How do you give solenoid stronger field

A

More turns
More current
Iron core

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15
Q

What is current

A

the movement of positive charge

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16
Q

Why does a current in a magnetic field produce a force

A

Field from wire and magnetic field interract (lines want to straighten) therefore force

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17
Q

How to know direction?

A

Flemings LH rule

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18
Q

Describe Flemmings LH rule

A

thumb motion
1st field
2nd current

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19
Q

Describe the relationship between force and magnetic flux density

A

Force is proportional to the current, magnetic flux density, and the length of the wire WITHIN the field

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20
Q

What is magnetic flux density

A

Strength of magnetic field

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21
Q

Symbol and Unit for magnetic flux density

A

B [Teslas] or [N/m/A]

22
Q

Experiment to determine magnetic flux density

A

Scales and wire and magnetic

23
Q

What is a Helmholtz coil

A

Solenoid pulled apart

~ uniform field in middle

24
Q

if a electron is moving through a magnetic field…

A

Treat current going the other direction

25
Q

When does F=BQv apply

A

when particle is moving perpendicular to field

26
Q

Describe movement of charged particle in magnetic field

A

Force is perpendicular
Velocity does not change
Direction changes
Circular motion

27
Q

What can act as a centripetal force

A

the force due to the magnetic field on a charged particle

28
Q

Describe a velocity selector is like

A

Magnetic field and electric field with a charged particle going through it

29
Q

How does a velocity selector work

A

only particles that are in equilibrium travel straight through
BQv=EQ

30
Q

What is v in the velocity selector

A

E/B ratio of electric to magnetic fields

31
Q

what is a potential difference not

A

a current

32
Q

How does a spectrometer work

A

velocity is selected
go through a magnetic field
radius depends on mass of particle as everything else is constant

33
Q

What is the principle of induction

A

a magnetic field and force can induce a current

34
Q

Why does induction occur

A

conservation of energy- electrons in wire experience a magnetic force causing them to move a current to be induced

35
Q

What is magnetic flux

A

product of magnetic flux density (perpendicular) and the cross sectional area of the coil

36
Q

What is the unit and symbol for magnetic flux

A

phi

Weber (Wb)

37
Q

SI for Wb

A

T/m^2

38
Q

What is magnetic flux linkage

A

N*phi - product of the number of turns in the coil and the magnetic flux of each

39
Q

What is Faraday’s Law

A

Magnitude of EMF produced is directly proportional to the rate of change of flux linkage

40
Q

What is lenz’s Law

A

Direction of EMF induced is always in the direction to oppose the change producing it

41
Q

Is it a n or s pole at the end of solenoid if the magnets n-pole is moving away

A

South

42
Q

Why is the constant of proportionality in Faraday’s Law -1

A

Lenz’s Law

43
Q

Why does Lenz’s Law occur

A

to ensure energy is conserived as work is done to move magnet

44
Q

What does EMF look like on graph

A

Sinusoidal

45
Q

Why is there alternating current from induction

A

As flux linkage = BAN cos(theta)

angle changes as inserted

46
Q

Describe a Transformers

A

two coils of wire around a soft iron core

47
Q

Why do transformers work

A

AC produces varying magnetic flux

this induces an EMF which induces a current in the wire

48
Q

Turns on a step up transformer

A

More turns on secondary

49
Q

Describe a step up transformer

A

raises voltage

50
Q

turns on a step down transformer

A

more turns on primary

51
Q

What do you remember about ideal transformers

A

Power is conserved - VI = VI

52
Q

To improve transformers

A

laminated soft iron core (reduces eddy currents)

low resistance reduces energy as heat lost

Physics A level OCR (23 decks)

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