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A-Level PHYSICS Edexcel > quantum > Flashcards

quantum Flashcards

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1
Q

What did planck work on?

A
  • He looked at black body radiation
  • He theorised that radiation was emitted in discrete packets of energy
  • he found there was a link between energy and frequency
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2
Q

What is a Quanta?

A

discrete packets of energy

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3
Q

E = hf

A

the equation which planck made, he had to make the constant h = 6.63 x10^-34 for it to work

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4
Q

What did einstein theorise?

A

That concentrated packets of energy had particle like properties and were called photons

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5
Q

photon

A

concentrated discrete packets of energy which have particle like properties

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6
Q

What is the EM spectrum from a particle point of view?

A

many photons with different levels of energy

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7
Q

How much do photons weigh?

A

weightless

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8
Q

how can photons travel at the speed of light?

A

because theyre weightless

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9
Q

what letter represents the speed of light?

A

c

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10
Q

how is the equation E = hc/ lambda formed?

A

combining E=hf and c=fλ

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11
Q

Electron volt

A

One electronvolt is the energy gained bu an electron when it is accelerated through a p.d. of 1v (W= QV)

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12
Q

how to convert joules to eV

A

divide by 1.6x10^-19

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13
Q

how to convert eV to Joules

A

multiply by 1.6x10^-19

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14
Q

how to find plancks constant?

A
  • set up a potential divider circuit with a paralell section with different coloured LEDs, an ammeter and a voltmeter
  • measure the voltage and record the wavelength (read from packet)
  • plot a graph of v agaisnt 1/λ
  • the gradient equals Vλ
  • substitute E = eV into E =hc/λ input values and rearrange to get h
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15
Q

Who worked out the photoelectric effect?

A

einstein

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16
Q

What is the photoelectric effect?

A

the emission of electrons from the surface of, generally, a metal in response to incident light.

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17
Q

What shows the photoelectric effect?

A

when a charge is given to an electroscope they repel each other so the gold leaf will lift and move away from the metal pole.

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18
Q

How can the charge of an electroscope be found?

A

the angle the gold leaf lifts too

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19
Q

why does the wave model no backup the photoelectric effect?

A

all the frequencies should combine energy to liberate the electrons

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20
Q

how many photons can liberate a single electron?

A

ONE

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21
Q

if wavelength increases…

A

frequency decreases therefore electrons have less kinetic energy and eventually none are liberated

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22
Q

if wavelength decrease

A

frequency increases therefore electrons have more kinetic energy

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23
Q

if intensity increases

A

more electrons are increased but with the same kinetic energy. if it is below the threshold frequency intensity has NO effect

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24
Q

electrons are trapped inside __________ and in order to escape it has to _________

A

energy wells

absorb enough energy

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25
Q

How does the material effect the energy well?

A

different sizes therefore different amounts of energy are needed to liberate the electrons

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26
Q

work function

A

the amount of energy needed for the electrons to escape their energy well

27
Q

which formula works out the work function

A

hf = Φ + E.K. max

28
Q

if the electron is given just enough energy to release from the energy well its kinetic energy equals 0 therefore….

A

threshold frequency can be found by Φ/h

29
Q

it doesn’t matter how many IR photons land on the metal… if

A

all of them are below the freshold frequency no single electron will be liberated

30
Q

photoelectron

A

a liberated electron

31
Q

intensity is proportional to

A

rate of emmision of photoelectrons

32
Q

Broglie

A

said that for any particle that had momentum it also has wavelength λ = h/p

33
Q

relativistic mass

A

as a particle gets closer to the speed of light the mass tends to increase due to relativistic effects

34
Q

The intensity of a wave at a point represents

A

the probability of a wave being there

35
Q

the electrons have _____ different energy levels by its energy is _______

A

infinite

finite

36
Q

how do you work out the energy changes of an atom?

A

calculate the frequency and wavelength needed to give the energy to move up levels and equally how much is emitted when it falls back down levels

37
Q

emission spectra

A

shows the certain wavelengths of photons which are given off by an element after it is excited and the electrons drop back down to there original energy levels ad emit energy

38
Q

absorption spectra

A

where certain frequencies of light are missing because they’re being absorbed by that element

39
Q

Threshold frequency

A

the lowest frequency of light at which electrons are still released from a surface

40
Q

wave equation

A

v = fλ

41
Q

what experiment determines the work function of different materials and the value of h?

A

stopping voltage experiment

42
Q

What does the graph from the stopping voltage experiment show?

A

gradient = h
F0 (x intercept) = threshold frequency
y intercept = work function

43
Q

What does the y intercept from the stopping voltage experiment show?

A

the voltage needed to stop an electron being liberated by light of 0 frequency and so 0 energy (the work function)

44
Q

What axises are plotted from the stopping voltage experiment?

A 
y = stopping voltage 
x = frequency
45
Q

what direction does current flow?

A

positive to negative (out the small end)

46
Q

what direction do electrons from?

A

negative to positive

47
Q

if the p.d. in a stopping voltage experiment is increased what happens?

A

electrons are accelerated faster as they move in the same direction as the current

48
Q

if the pd. in a stopping voltage experiment is decreased what happens?

A

the battery is more effective than the photoelctric effect therefore the electrons are slowed and start to move backwards.

49
Q

what is stopping voltage?

A

the voltage at which the battery becomes more powerful than the photoelectric effect and the electrons are slowed

50
Q

electric field

A

as the electric force per unit charge.

51
Q

How how does an electron gun create a beam of electrons?

A

A hot filament causes thermionic emmision of electrons. the electrons at repelled away from the the negative electrode and towards the positive electrode causing an accelerating force. Collimation takes place as the electrons are forced through a small gap. There must be a vacuum.

52
Q

How are ions accelerated

A

Electeic fields exist between positive and negative electrodes implying a force on the the ions causing acceleration

53
Q

Force = rate of change of

A

Momentum

54
Q

Why are electrons only emitted about a threshold frequency?

A

Photon energy is proportional to frequency therefore photon energy must be greater than the work function to liberate an electron. All the energy must come from a single electron.

55
Q

Line spectra

A

Specific frequencies/wavelengths show the absorbtion/ emmision lines within a narrow line of wavelengths

56
Q

How do line spectra provide evidence for the existence of energy levels in atoms

A

Photons associated with particular energies show electron transitions up and down the discrete energy levels to provide the line spectra

57
Q

Kinetic energy gained by accelerating electron through a potential difference =

A

eV

58
Q

Why are only certain frequencies absorbed by atoms?

A

electrons can only exist in discrete energy levels

59
Q

ground state

A

the lowest energy level where electrons are usually found

60
Q

energy delivered by photon (hf) =

A

difference between the energy levels

61
Q

how can electrons be excited?

A
  • if a photon is absorbed

- if electrons are hit be other electrons

62
Q

how is a photon emitted

A

electrons don’t remain in an excited state so they de-excite and drop down to the ground state and emit energy in the form of a photon

63
Q

high frequency photon means…

A

the more energy levels it jumps up

64
Q

long wavelength photon means…

A

less energy levels moved up

A-Level PHYSICS Edexcel (16 decks)

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