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higher physics > electricity > Flashcards

electricity Flashcards

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1
Q

T in calculation

A

T=horizontal divisions x the time base setting (usually in ms)

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2
Q

voltage is determined by

A

number of vertical divisions (amplitude x y gain)

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3
Q

Vrms

A

the value that produces the same effect as an equivalent value a.c. supply

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4
Q

the peak value is always higher than…

A

the rms value

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5
Q

rms

A

root mean square

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6
Q

a voltage divider

A

a circuit with 2 series resistors/bulbs etc.

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7
Q

the size of the voltage across each resistor depends on…

A

the size of the resistors

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8
Q

if the resistors are the same

A

then they both have an equal share of the supply voltage

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9
Q

when no current flows

A

the t.p.d. = emf

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10
Q

as the resistance of the variable resistors decreases

A

more current is drawn form the battery so the current and the t.p.d. increases

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11
Q

lost volts

A

volts that are lost in the internal resistance of the battery itself as it heats up

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12
Q

emf =

A

t.p.d. + lost volts

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13
Q

in a graph, the gradient is

A

m= -r

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14
Q

emf

A

the electric potential energy supplied to each coulomb of charge which passes through the source

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15
Q

emf stands for

A

electromotive force

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16
Q

the lost volts are the

A

voltage available to the circuit

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17
Q

t.p.d.

A

the voltage available to the circuit, what is across the load resistor (sometimes more than one resistor)

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18
Q

capacitors

A

two conducting layers separated by an insulator which can store charge

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19
Q

charge can be stored

A

by connecting the capacitor to a d.c. source, electrons leave the positive plate and are added to the negative plate

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20
Q

capacitance

A

a measure of the charge it can store for every volt across it

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21
Q

the time taken for a capacitor to charge up and discharge depends on:

A

the size of the capacitor and the resistance of the circuit

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22
Q

when a capacitor is fully charged

A

the voltage across it is equal to the supply voltage

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23
Q

when a capacitor discharges

A

charge moves off the plates in the capacitors in the opposite direction to the way it moved onto the capacitor

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24
Q

conductor

A

a material for which an applied voltage causes a current to flow, the current is proportional to the voltage (ohm’s law)

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25
Q

insulator

A

a material for which an applied voltage causes very little current, the current remains very small until the voltage becomes very large

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26
Q

semiconductor

A

really just an insulator, but where the voltage needed to drive a current is smaller than usual

27
Q

the two highest energy bands are known as

A

the conduction bands and the valence bands

28
Q

the valence band is

A

always completely full of electrons, these electrons are not free to move

29
Q

the conduction band is

A

the higher band, any electrons in this band are free to move and allow the material to conduct

30
Q

the gap between the valence band and the conduction band is called

A

the band gap

31
Q

if there are free electrons in the conduction band

A

the solid will conduct

32
Q

in an n-type semiconductor

A

the free charge carriers are negatively charged electrons

33
Q

in a p-type semiconductor

A

these holes are just above the valence band in the atoms

34
Q

at the junction

A

electrons from the n-type move across into holes in the p-type

35
Q

p-type in a junction

A

slightly negatively charged

36
Q

n-type in a junction

A

slightly positively charged

37
Q

the barrier potential

A

a small voltage across the junction, typically around 0.7V

38
Q

why would red LED show when the ammeter gives a +ve reading and the green LED show when the ammeter gives a -ve reading

A

LEDs will light when they are forward biased, the change in polarity of voltage changes the biasing

39
Q

the gap between the valence band and the conduction band in semiconductors is

A

smaller than in insulators

40
Q

use band theory to explain how an LED emits light

A

electrons move towards conduction band of p-type, then drop from conduction band to valence band and a photon is emitted

41
Q

photovoltaic effect

A

a potential difference is produced when photons enter the layer between the p-type and n-type materials

42
Q

why, in terms of photons, would the maximum output power increase if a lamp is moved closer to the solar cell

A

greater number of photons per second

43
Q

why may batteries not work with some LED colours, in terms of band theory

A

the electrons do not gain enough energy to move towards the conduction band of the p-type

44
Q

forward bias of LED

A

conducts and emits light

45
Q

band theory

A

electrons are excited from the valence band to the conduction band of the n-type semiconductor. the electron will conduct to the conduction band of the p-type, drop to the valence band as it loses energy in the form of a photon

46
Q

lost volts decrease with

A

current

47
Q

when frequency changes what happens to the current

A

nothing

48
Q

initial current only depends on

A

the EMF and resistance

49
Q

what effect does adding impurity atoms have on resistance of the material

A

decreases it

50
Q

an n-type semiconductor is formed by

A

adding impurity atoms to a sample of pure semiconductor material

51
Q

maximum discharge current

A

V=IR with total resistance and EMF

52
Q

use band theory to explain how a potential difference is produced when photons are incident on the photodiode

A

electrons gain energy from photons and move from the valence band to the conduction band. electrons move towards n-type semiconductor

53
Q

photovoltaic effect

A

when a photodiode produces a potential difference when photons are incident on it

54
Q

explain why the charging current decreases as the battery charges

A

the emf of the battery increases so the difference between the two emfs decreases

55
Q

explain why current decreases with time when a capacitor discharges

A

the voltage decreases

56
Q

use band theory to explain why semiconductors might conduct at room temperature

A

the band gap is small so some electrons have enough energy to move from the valence band to the conduction band

57
Q

alternating current

A

changes direction and value with time

58
Q

conduction in an n-type semiconductor is by

A

the movement of free negatively charged electrons

59
Q

solar cells cause the

A

photovoltaic effect

60
Q

LEDs are

A

forward biased p-n junction diodes that emit photons when electrons fall from the conduction band into the valence band of the p-type semiconductor

61
Q

why might the voltage reading decrease when the switch is closed (if it is originally short circuit)

A

there is now a current so voltage is less across the internal resistance

62
Q

short circuit current

A

maximum current

63
Q

doped semiconductor

A

a semiconductor that has impurities added

higher physics (4 decks)

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