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Yr 10-11 Physics > Unit 4 > Flashcards

Unit 4 Flashcards

1
Q

what do opposite poles do

A

attract

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2
Q

what to do similar poles do

A

repel

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3
Q

what direction do magnetic field lines always point

A

north to south

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4
Q

in attraction, how do the field lines point

A

they point north to south and flow between the 2 points

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5
Q

in repulsion, what is the nature of the field lines

A

they point in opposite directions and bend away from each other

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6
Q

how is the strength of the magnetic field seen

A

the density of the field lines

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7
Q

what happens when permanent magnets attract a magnetic materia

A

a magnetic field is induced in the material

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8
Q

what does hard magnetic materials mean

A

they are hard to magnetise and also hard to demagnetise

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9
Q

what does soft magnetic materials mean

A

they are easy to magnetise and demagnetise

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10
Q

what is an electromagnet

A

when a coil of wire carries current and a magnetic field is induced

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11
Q

what are properties of permanent magnets

A

constant magnetic field
cannot be switched on and off
north and south poles cannot be switched
made with hard magnetic materials

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12
Q

what are properties of electromagnets

A

variable strength magnet field
can be switched on and off quickly
north and south poles can be changed by changed the direction of current flow
made from soft magnetic materials

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13
Q

what are the charge carriers in electrical devices

A

electrons

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14
Q

why are conductors able to conduct

A

there electrons are free to move around

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15
Q

why are insulators unable to conduct

A

there are no free electrons to move

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16
Q

what is a charge

A

an electric charge that can be positive or negative

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17
Q

what do unlike charges and like charges do

A

unlike charges attract
like charges repel

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18
Q

what happens if there is an equal number of positive and negative charges

A

it is neutral

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19
Q

what happens when an object loses electrons

A

it becomes positively charged

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20
Q

what happens when an object gains electrons

A

it becomes negatively charged

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21
Q

what is the symbol for electrical charge and how is it measured

A

symbol is Q
measured in coulombs(C)

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22
Q

what is static electricity

A

occurs when friction between 2 insulators causes electrons to be transferred from one surface to another

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23
Q

what are electrical fields

A

when 2 charged particles approach each other, they experience a force
the space in which the electric charge experiences a force is called the electric field

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24
Q

what is current

A

the measure of the flow of charge
also known as rate of flow of charge

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25
how can current be increased
current flow can be increased by: making each charged particle move faster increase the number of charged particles increased the amount of charge each particle carries
26
formula for current
I = Q/T current = charge/time
27
what is used to measure current
an ammeter
28
what is conventional current
electrons are repelled from the negative terminal of the battery and attracted to the positive terminal conventional current is the opposite(positive to negative)
29
what are alternating currents(AC)
when the electrons continously change direction
30
what are direct currents(DC)
electrons flow in one direction
31
what is electromotive force
the phenomena that enables charge to flow around the whole circuit determined by the battery voltage
32
what is electromotive force measured in
volts
33
what is potential difference
the energy needed per charge to flow between two points in a circuit work done per unit charge
34
what is potential difference measured with
measured with a voltmeter and always placed parallel across a component
35
formula for potential difference and electromotive force
V = W/Q v = voltage w = energy q = charge
36
what is resistance
the measure of how much opposition there is to the flow of current measured in ohms
37
what is the formula for resistance
R = V/I r = resistance v = potential difference i = current
38
how is the length of the wire related to resistance
resistance is directly proportional to the length of the wire
39
how is the thickness of the wire related to resistance
it is inversely proportionate thicker the wire, smaller the resistance
40
what is ohms law
electric current is directly proportionate to voltage and inversely proportionate to resistance
41
how can electrical power be calculated
P = IV p = power i = current v = potential difference
42
what is a diode
only allows current to flow in one direction requires a small amount of power to activate non ohmic device
43
what is a light emitting diode(LED)
regular diode that lights up when current flows through
44
what is a series circuit
the current flows in one loop and voltage is shared throughout. if there are multiple lamps, they will all be dimmer
45
what is a parallel circuit
there is more than one loop of current voltage is the same for all loops
46
advantages of parallel circuits
the potential difference across each lamp will be equal to the e.m.f. means every lamp will be brighter each loop can be turned off separately
47
featurs of series circuits
the current will be the same at all points the potential difference across all resistors is shared sum of the pd = battery power
48
how to find total resistance in series circuits
by adding resistance of all the components up
49
features of parallel circuits
the current flowing into a junction is equal to the sum of currents flowing out of a junction each resistor experiences the same p.d as the power supply
50
how to find total resistance in parallel circuits
1/total resistance = 1/resistance of component 1 + 1/resistance of component 2
51
what is Faradays law
a wire close to a changing magnetic field will experience an induced electromotive force
52
how can EMF be induced
moving a magnet so that its field lines are cut by the wire moving a wire across a magnetic field
53
what is flemings right hand rule
thumb is direction of motion of the wire first finger is direction of magnetic field second finger is direction of the current
54
what is Lenz's law
the direction of the induced emf opposes the charge that creates it
55
how can the strength of the induced emf be increased
increasing the force or speed at which the wire or hte magnet is moved increasing the strength of the magnet
56
what happens when the wire moves parallel to the magnetic field
an emf is not induced
57
how can the induced emf be decreased
decreasing the number of turns in the wire
58
how do AC generators work
a rectangular coil of wire continously rotates within a magnetic field and generates an induced emf the slip rings allow the direction of the induced emf to alternate and cause an ac currect
59
what is the purpose of carbon brushes in AC generator
make an electrical connection between the rotating coil and circuit
60
what will the voltage output look like in an AC generator
the voltage output will have peaks and troughs as the magnet turns from being parallel to perpendicular
61
what magnetic field does a direct current create
it creates a constant magnetic field
62
what magnetic field does an alternating current create
an alternating magnetic field
63
what is the magnetic field around a current carrying wire
circular
64
whats a solenoid
when wires are arranged in a coil, the resulting magnet is the same is that of a bar magnet
65
how can the magnetic field of a solenoid be made stronger
increase the current through the solenoid increase the number of turn in the wire
66
what happens when the solenoid is supplied with an alternating current
changes the direction of the magnetic field every half cycle
67
what happens when a current carrying wire is placed within a magnetic field
the wire experiences a force and can move
68
how can the size of the force be increases when a current carrying wire is placed in a magnetic field
increase the current in the wire increase the number of individual wires increase the strength of magnetic field increase the length of the wire
69
what is the right hand rule used for
used to find emf induction
70
what is left hand rule used for
used for DC motors
71
what is the difference between AC and DC motors
DC motors have a cell that supply it power AC motors get their current through an induced emf
72
how can DC motors spin quicker
increase the strength of the magnetic field increase the number of turns of wire in the coil increase the current to the coil from the power supply
73
what are transformers
device that can increase or decrease the size of an alternating electromotive force
74
what do step up transformers do
increase the voltage
75
what do step down transformers do
decrease the voltage
76
what do transformers consist of
a primary coil- alternating current supplied through her soft iron core-allows transition of magnetic flux to a secondary coil a secondary coil-the output of the transformer and will have more or less coils
77
formula for transformers
Vp/Vs = Np/Ns Vp-voltage applied to primary coil Np-number of turns in the coil Vs-voltage applied to secondary coil Ns- number of turns
78
how many turns does the secondary coil have in a step up
the secondary coil has more turns than the primary coil
79
how many turns does the secondary coil have in a step down transformer
has fewer turns than the primary coil
80
what current do transformers require
they require alternating currents
81
what is formula for 100% efficiency in a transformer
IpVp = IsVs
82
how can the efficiency of a transformer increase
using low resistance coils to reduce power wasted using a laminated core which consists of layers of iron separated by layers of insulation
83
how can power loss in a wire be calculated
P=1^2R

Yr 10-11 Physics (7 decks)

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