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physics > electricity > Flashcards

electricity Flashcards

1
Q

what does an ammeter read?

A

current measured in A

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2
Q

equation for charge, currrent, and time

A

Q= It

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3
Q

what is voltage?

A

energy given to each coulomb of charge passing through a power supply

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4
Q

what is voltage also known as?

A

potential difference

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4
Q

equation for energy given to each coulomb of charge (or work done to fully charge a capacitor)

A

W= QV

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4
Q

ohms law formula

A

V= IR

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5
Q

equation for power from current flowing and potential difference

A

P= IV

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6
Q

potential dividers formula

A

V= (R1/ R1+R2) x Vs

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7
Q

equation for power, energy, and time

A

P= E/t

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8
Q

DC signals current direction

A

one direction only

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9
Q

AC signals current direction

A

changes direction periodically

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10
Q

what does the y-gain of an oscilloscope tell you?

A

voltage value per box

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11
Q

what does the time base (x) of an oscilloscope tell you?

A

how long wave takes to cover one box in x-direction

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12
Q

peak voltage equation

A

pv= no divs x y-gain

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13
Q

period of wave equation

A

T= no divs x timebase

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14
Q

frequency equation

A

f= 1/ T(period)

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15
Q

notation for time base

A

10^-3

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16
Q

v peak formula

A

vpeak= √2 x Vrms

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17
Q

I peak formula

A

ipeak= √2 x Ims

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18
Q

when can you use V= IR?

A

using both peak voltage in current

or

using both rms voltage and current

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19
Q

what is EMF?

A

the electromotive force of a source is;

energy supplied to each coulomb of charge passing through the source

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20
Q

what happens when the switch in a circuit is open?

A

no current flows and voltmeter reads EMF

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21
Q

what are lost volts?

A

energy wasted inside a source due to its internal resistance

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22
Q

lost volts formula

A

V= Ir

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23
Q

what is terminal potential difference?

A

voltage that remains after lost volts are subtracted from the EMF

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24
Q

EMF formula

A

E= V= Ir

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25
Q

what happens in a short circuit?

A

external resistance effectively zero

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26
Q

what happens due to a short circuit in E= Ir?

A

current is incredibly high

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27
Q

why is the EMF and terminal potential difference different?

A

current flowing with switch closed means r must be considered and there are lost volts

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28
Q

parallel resistors formula

A

1/Rt= 1/R1 + 1/R2

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29
Q

what happens to the voltmeter reading if all resistors are connected in parallel?

A

total external resistance decreases

voltmeter reading decreases

current flowing increases

lost volts increases

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30
Q

what 2 things does a graph of 1/i against R give?

A

gradient gives EMF

y-intercept gives -r

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31
Q

what 2 things does a graph of V/i give?

A

gradient gives -r

y-intercept gives EMF

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32
Q

how do you find the short circuit current?

A

where line cuts x axis

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33
Q

what is a capacitor?

A

a device designed to store charge

34
Q

what is capacitance measured in?

A

farads

35
Q

micro-farad notation (μF)

A

1x10-⁶

36
Q

nano-farad notation (nF)

A

1x10-⁹

37
Q

what happens when capacitor is fully charged?

A

potential difference has reached the same point as supply voltage

38
Q

what happens in the directly proportional relationship between a capacitor and voltage?

A

the more charged a capacitor is, the higher the potential difference across the capacitor

39
Q

equation for capacitance

A

C= Q/V

40
Q

how is the energy stored in a capacitor found?

A

area under a graph

41
Q

energy stored in a capacitor formula

A

E= ½QV

42
Q

when is the only time E= ½QV can be used?

A

energy in a capacitor

43
Q

why is the work done to fully charge a capacitor and the energy stored in a capacitor different?

A

only half work is used to charge capacitor

other half given off as heat in resistor R

44
Q

what is a smoothing capacitor?

A

smooth or even out fluctuations in a signal

45
Q

electron availability in conductors, insulators, and semi- conductors

A

conductor- many free electrons

insulator- very few free electrons

semiconductor- very few free electrons when pure, but conduct when impurities present

46
Q

2 examples of semi-conductors

A

silicon

germanium

47
Q

2 highest energy bands in order

A

conduction band

valence band

48
Q

when will a solid conduct?

A

when there are electrons in the conduction band

49
Q

band theory in an insulator

A

valence band completely full- electrons can’t move

energy/ band gap is large so electrons can’t gain enough energy to move up to conduction band

50
Q

band theory in a semi- conductor

A

valence band completely full

energy/ band gap is small so electrons can move up to conduction band if they gain enough energy, and then be free

51
Q

band theory in a conductor

A

valence and conduction band usually overlap, meaning electrons free to move

52
Q

what are intrinsic semiconductors?

A

have four outer electrons

all outer electrons are bonded so there are very few free electrons- making for a large resistance

53
Q

2 places electrons come from in intrinsic semiconductors

A

imperfections in the lattice

thermal ionisation due to heating

54
Q

what happens when temperature increases in intrinsic semiconductors?

A

produces more free electrons

55
Q

2 changes due to increased temperature in intrinsic semiconductors

A

conductivity increases

resistance decreases

56
Q

what is a positive hole?

A

when an electron leaves its space in the valence band and leaves a space that is positively charged

57
Q

what may happen to this hole?

A

may be filled by electron from neighbouring atom

this would then leave its own hole

58
Q

what happens if an impurity atom with 5 outer electrons is present in the lattice?

A

an extra free electron is introduced

59
Q

2 effects of the 5 outer electron impurity atom

A

conductivity increases

resistance decreases

60
Q

what is this process of adding an impurity atom called?

A

doping

61
Q

why is it called an n-type semiconductor?

A

majority charge carriers are negatively charged electrons

62
Q

where does this extra electron from the n- type semiconductor lie?

A

within the band gap- but a small amount of energy away from jumping to the conduction band

63
Q

example of a 5 outer electron impurity atom

A

arsenic

64
Q

example of a 3 outer electron impurity atom

A

indium

65
Q

what happens when a 3 outer electron impurity atom is introduced to the lattice?

A

hole is introduced where an electron is missing

66
Q

how can conduction take place in a 3 outer electron impurity atom?

A

electrons from adjoining atoms through the movement of positive holes created

67
Q

why is it called a p-type semiconductor?

A

majority of charge carriers are positively charged holes

68
Q

what does the small potential difference across the junction do?

A

opposes any further movement of charge

69
Q

what occurs in the region around the junction?

A

there is no charge and is an insulator

called the depletion layer

70
Q

what does “biasing” a semiconductor device mean?

A

apply voltage to it

71
Q

2 ways of semiconductor bias

A

forward biased

reverse biased

72
Q

what happens in a forward bias?

A

electrons attracted to positive terminal of battery

holes will be attracted to negative terminal of battery

current flows

73
Q

what happens in a reverse bias?

A

electrons move toward positive terminal

holes move toward negative terminal

depletion layer grows

no current flows

74
Q

what does the result of a reverse bias mean for current and what is this known as?

A

it can only flow one way

diode

75
Q

what is an LED?

A

consist of p-n junction diode connected to a positive and negative terminal

76
Q

what is the difference between a p-type and an n-type semiconductor and why?

A

p-type semiconductor valence and conduction bands are higher up

due to electrons needing higher energies to jump to conduction band

77
Q

3 movements describing how and LED works

A

electrons at junction move from n-type to p-type conduction band

holes move from p-type to n-type valence band

electrons drop down to valence band to fill holes

78
Q

what happens when the electrons drop?

A

photon is emitted

79
Q

what does the colour of light emitted from photon when electrons drop depend on?

A

band/energy gap

bigger the band/energy gap, the higher the frequency of light emitted

80
Q

what is a photodiode?

A

a p-n junction with a transparent coating that reacts to light

81
Q

what happens when light of a higher energy than the band gap falls on the junction and what is produced?

A

excites an electron from the valence band and into the conduction band

leaves behind a hole

electron-hole pair produced

82
Q

what happens after electron-hole pair made and what is produced?

A

electron accelerated into n-type

hole accelerated into p-type

photocurrent produced

83
Q

what is happening as this photocurrent is produced?

A

light energy being converted to electrical energy

84
Q

what can this photodiode be used as and what is this the basis of?

A

as a power source

basis of a solar cell

85
Q

full photovoltaic effect process

A

light of higher energy than band gap falls on junction

this excites electron from valence into conduction band, leaving behind hole, producing electron-hole pair

electron accelerated into n-type and hole to p-type

this causes photocurrent to be produced

light energy converted to electrical energy

photodiode used as power source- basis of solar cell

physics (4 decks)

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