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BMAT Physics > Electricity > Flashcards

Electricity Flashcards

(81 cards)

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1
Q

electric current definition

A

flow of charge
rate of movement of charge
will only flow through a component with potential difference across it

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2
Q

cell definition

A

single electrical energy source

supplies circuit with power, provides potential difference

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3
Q

how cell applies potential difference to circuit

A

transfers energy to charges passing through cell

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4
Q

voltage definition

A

potential difference

electrical pressure that causes current to flow in a circuit

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5
Q

potential difference formula

A 
potential difference (volts) = work done (J) / charge (C)
V = W/Q
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6
Q

current formula

A

current (A)= charge (C) / time(s)

I = C/t

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7
Q

resistance definition

A

how difficult for charge to flow through it

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8
Q

resistance formula

A

resistance (ohms, omega)= potential difference (V) / current (A)
R = V/I

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9
Q

how to measure resistance

A

connect ammeter before component

voltmeter across both ends of it

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10
Q

Ohm’s law

A

ratio of voltage to current is constant

R = V/I

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11
Q

ohmic conductor definition

A

conductor that obeys Ohm’s law

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12
Q

current-voltage graph of ohmic conductor

A

straight line as resistance is fixed
resistance is equal to inverse of gradient of line
steeper graph, lower resistance

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13
Q

filament lamp current-voltage graph

A 
more current = more heat = more resistance 
as resistance increases with current, gradient decreases to reflect this
curved graph (looks like S, sigmoid)
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14
Q

power definition

A

rate of energy transfer

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15
Q

power formula

A

P (W) = E (J) / t (s)

power = work done / time taken

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16
Q

power (electricity) formula

A

power (W) = potential difference (V) x current (A)

P = I x V

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17
Q

static electricity

A

insulating materials rubbed together
electrons rubbed off one material and deposited to other material
charges build up
spark/shock happens when enough charges build up and move
material that gains electrons become negative and vice versa

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18
Q

direction of electron transfer in static electricity

A

depends on material
examples:
cloth duster -> polythene
acetate -> cloth duster

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19
Q

static electricity in medicine

A

defibrillators

produced electrical shocks, makes heart contract when placed on patient’s chest

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20
Q

static electricity in dust precipitates

A

dust precipitators remove dust from chimneys
cleans emissions from factories
negatively charged grid in chimneys makes dust particles negative
-ve particles attracted to +ve metal plates, form large particles

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21
Q

static electricity in paint sprayers

A

paint charged so droplets repel each other
gives fine spray
surface being painted given opposite charge to attract paint droplets
gives even coat + less waste

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22
Q

switch function

A

opens/closes circuit

allows current to flow or not flow through it

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23
Q

cell/battery function

A

battery = series of cells
supplies circuit with power
provides potential difference needed to move charge around circuit

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24
Q

lamp function

A

thin wire in inert gas

wire gets hot and flows when current flows through

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25
fuse function
stop current from flowing through circuit when current gets very high (melts and opens circuit)
26
diode function
only allows current to flow in one direction | restricts current in parts of circuit
27
light-emitting diode function (LED)
only allows current to flow in one direction | glows when current flows through it
28
fixed/variable resistor function
oppose flow of current | helps set current in circuit to wanted value
29
thermistor function
temperature-dependent resistor | changed resistance according to temperature
30
voltmeter function
measure potential difference in volts across given component always in parallel with components
31
ammeter function
measure current in amps in component | placed in series with components
32
light deadens resistor function (LDR)
resistor changing resistance depending on amount of light shining on it
33
current across a series circuit
same at any point in the circuit
34
potential difference across series circuit
potential difference shared between components
35
energy transferred from battery in circuit
total energy transferred from battery to charge = total energy transferred from charge to components
36
resistance across series circuit
resistance of circuit = sum of resistance of each component
37
current across parallel circuit
current shared between components of circuit
38
potential difference across parallel circuit
potential difference is same at any point of circuit
39
resistance in parallel circuits
more components = in parallel = lower total resistance p each individual circuit gives electrons more than one way to get around circuit also provided higher current
40
efficient versions of filament light bulbs
compact fluorescent lamps (CFLs) | light-emitting diodes (LEDs)
41
how to save money with electricity
some electricity is converted to waste energy | using more efficient appliances keeps this to a minimum, decreases energy bill in long term
42
magnets definition
objects that produce magnetic field | have opposite north and south poles
43
hard magnets definition
permanent magnets generate own magnetic field able to maintain it constantly
44
examples of hard magnets
pure iron nickel cobalt steel
45
soft magnets definition
induced magnets objects that generate magnetic field only if within magnetic field can only be attracted by other magnets, cannot be repelled permanent magnets induces only opposite pole on soft magnets
46
soft magnet examples
some alloys of iron and other magnetic metals | iron fillings
47
electromagnetic effect definition
circular magnetic field generated around wire when wire carries current
48
direction of magnetic field in straight wires
anti-clockwise and perpendicular to direction of current
49
direction of magnetic field in solenoids
south pole at positive end north pole at negative end like a bar magnet
50
how to increase strength of magnetic field around wire
``` increase current (directly proportional) increase number of coils in solenoid (each coil has own magnetic field, adding coils increases amount of individual magnetic field) ```
51
permanent magnets vs electromagnets
permanent magnet retains magnetism once magnetised | electromagnet only has magnetism when current passes through it
52
what is produced when wire’s magnetic field interacts with permanent magnetic field
force
53
Fleming’s left hand rule
``` finger = direction of thumb = force index = magnetic field middle = current ``` used for motors
54
magnitude of force for straight wire in uniform field when all quantities are perpendicular) equation
force (N) = magnetic field stretch (T) x current (A) x length of wire (m) F = BIL
55
how DC motor works
DC current flows through armature on commutator between north and south pole permanent magnets overall turning motion as 2 opposite forces on two sides of coil
56
how to increase force produced in DC motor
more turns of coil stronger magnetic field stronger current longer length of wire
57
electromagnets in speakers
variation of input current in soil moved core at specific frequency via motor effect cone attached vibrates at same frequency generates pressure waves in air (produces sound)
58
electromagnets in microphones
same as speaker except in reverse | generator effect in place of motor effect
59
electromagnets in doors
entering correct passcode / using keycard disables electromagnet holding door close
60
electromagnets in toasters
magnet holds bread down | roast pops out when time is up and power to electromagnet is cut off
61
electromagnetic induction definition
product of a potential difference across an electrical conductor in a changing magnetic field
62
how potential difference can be induced in an electrical conductor
magnet moved into coil of wire | electrical conductor moved in a magnetic field not parallel to field lines
63
how direction of induced potential difference/current can be changed
changing direction of movement of conductor relative to magnetic field changing direction of magnetic field (polarity)
64
how AC current is induced
magnet moved backwards and forwards in the coil
65
how voltage is increased in induced AC currents
moving magnet faster stronger magnet more turns of coil higher area of coil
66
how AC generators work
induces current by spinning coil of wire inside magnetic field of magnet or vice versa current changes every half turn as direction of motion changes due to alternating current
67
how current and voltage increases in AC generator
strength of magnetic field number of turns of coil rate at which coil/magnet spins (also affects frequency)
68
Fleming’s right hand rule
``` finger = direction of thumb = force index = magnetic field middle = current ``` used in generators
69
output voltage of AC generators
generator effect only exists when wire is cutting field lines maximum when 90° or 270° as coil is most perpendicular to magnetic field lines 0 when coil is not cutting magnetic field lines (0°, 180°, 360°)
70
transformer definition
device that changes voltage of AC supply
71
step-up transformer
changes low voltage supply to high-voltage supply | increases voltage as more turns on secondary coil than first
72
step-down transformer function
changes high voltage supply to low voltage supply | increases voltage as less turns on secondary coil than first
73
Structure of transformer
primary and secondary coils wound around soft iron core (coils not connected to each other) primary coil supplies AC to iron core, induces magnetic field which is transferred to secondary coil where current is induced
74
relationship of voltages of primary and secondary coils
inversely proportional to each other
75
ratio of voltage across primary and secondary coils
depends on number of turns on primary and secondary coil | V1/V2 = N1/N2
76
power in coils formula
transformers nearly 100% efficient power in primary coil = power in secondary coil power = potential difference x current so V1 x I1 = V2 x I2
77
transformers in the national grid
high power supply = very high voltage or high current step-up transformers used to produce very high voltage and low current for transmission of electricity (minimises energy loss through heat) step-down transformers used to reduce voltage to safe value before arriving in homes
78
power loss due to resistance in cables formula
power loss (V) = current^2 (A) x resistance (ohms)
79
why high voltage is used
high power is made by high voltage or high current | increasing current instead of voltage for high power = more heat loss as power loss is dependent on current
80
switch more transformer
``` reduced voltage of main supply converts AC to DC operates at high frequency lighter and smaller used very little power when no device connected to output terminals ```
81
isolating transformer
same number of turns in primary and secondary coils same voltage used to isolate connections from mains

BMAT Physics (7 decks)

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