quantum Flashcards

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1
Q

explain why current in photocell only if frequency is above a certain value(3)

A
  • energy photon (1)

- greater than work function –so electrons emitted

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2
Q

effect on current of increased intensity radiation (2)

A
  • current greater (more electrons emitted per second)

- increased intensity = more photons incident per second

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3
Q

work function

A

energy required to remove electron

minimum energy required to remove an electron from metal surface

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4
Q

comparing x rays and UV - what can be said ?

A

same element, photoelectrons emitted using x rays have greater max energy

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5
Q

when light incident on metal surface photo cell increasing intensity of illumination at surface leads to increase

A

in current through photocell

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6
Q

why emitted electrons have range kinetic energies up to a maximum

A

energy of photon is constant / fixed OR energy given to electron is fixed
energy required for electron to leave / escape / emit from the surface / metal
OR electron has to overcome work function
maximum kinetic energy is the energy of photon minus the work function
deeper electrons require energy to get to the surface OR have less Ek than surface electrons

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7
Q

effect of decreasing frequency of incident radiation while keeping intensity constant on emitted electrons (2)

A

-decrease energy photons
-decrease maximum kinetic energy electrons
-

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8
Q

effect on emitted electrons double intensity + freq constant (2)

A
  • increase photons - increase in emitted electrons

- double number electrons emitted per second

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9
Q

why emitted electrons have range of ke to max 4

A

photons have energy dependent on frequency OR energy of photons constant
one to one interaction between photon and electron
Max KE = photon energy – work function in words or symbols
more energy required to remove deeper electrons

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10
Q

what must happen to validate new scientific theory (2)

A

theory makes predictions tested by repeatable/checked by other
scientists/peer reviewed (experiments) OR new evidence that is repeatable/
checked by other scientists/peer reviewed

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11
Q

why no photoelectric observed when potassium surface given positive charge (2)

A

surface attracts negative electron back to positive surface

photons have insufficient energy/energy required increased

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12
Q

explain why ke emitted has max value

A

hf is energy available / recieved from photons

energy required to remove electron varies

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13
Q

unit for work function

A

joules

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14
Q

why if freq below certain value electrons not emitted (2)

A
  • work function minimum energy to release electron

- below certain frequency energy PHOTON less than work function

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15
Q

when talking about freq/energy being less than work function always say

A

photons as well as electrons

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16
Q

when do E= hf its

A

in joules already

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17
Q

energy = 9.9x10-19 and light energy incident on each square mm of surface rate of 3x10-10 Js-1

A

number of photons per second = 3.0 × 10–10/9.9 × 10–19 (1)

number of photons per second = 3.0 × 108 (1)

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18
Q

time delay in liberating electron doesn’t occur - what happened with new evidence

A

light travels in quanta / photon

old theory rejected

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19
Q

state what is meant by threshold frequency

A

below a certain frequency (called the threshold frequency) no electrons emitted (1)
or minimum frequency for electrons to overcome work function

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20
Q

always say in frequency questions

A

ENERGY PHOTON DEPENDS ON FREQUENCY

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21
Q

why no photoelectric effect below threshold freq

A

(light travels as photons) energy of a photon depends on
frequency (1)
below threshold frequency (photon) does not have enough
energy to liberate an electron (1)

22
Q

assumption in increase intensity increases current

A

one photon liberates one electrons - more photons incident per second

23
Q

2 points why a light causes photoelectric

A

high frequency above threshold

24
Q

for excitation say

A

up

25
Q

ionisation

A

electron removed from atom

26
Q

describe what happens in an atom when line spectra produced (3)

A
  • electrons move(or excited) from one energy level(or orbit) to another (1)
  • emitting or absorbing a definite frequency / wavelength / colour (1)
  • photon energy(of electromagnetic radiation) (1)
27
Q

how are energy levels useful in explaining spectra (3)

A
  • only certain energies [or energy changes] allowed (1)
    a line [or photon] corresponds to transition between levels (1)
    each transition [or energy change]
    corresponds to a definite wavelength [or frequency] (1)
28
Q

for diffraction allowed size be within

A

same order magnitude (power of 10)

29
Q

piece of evidence for particle like properties

A

deflection in magnetic fields

30
Q

misconception on work function with electrons in metal

A

all electrons have same work function just deeper down require more WORK to reach surface and escape

31
Q

always say in electron level negative explanation

A

WORK DONE to excite electrons

32
Q

must result in energy being emitted from atom =

A

relaxation

33
Q

when talking about photon absorption to move to higher level

A

ALL ENERGY ABSORBED IN 1TO1 INTERACTION

34
Q

electron can only trasnfer

A

part of its energy - so will move off with excess kinetic energy

35
Q

if question says same nucleon number in long answer question then always say

A

same number protons and neutrons

36
Q

what to say for diff maximum kinetic energy’s

A

energy required to liberate electrons varies (not work function!)

37
Q

if work function mentioned in any question even if it seems like don’t mention it what do you do

A

define it - minimum energy for electron to be liberated

38
Q

when time delay doesn’t occur in photoelectric what does this prove

A

light travels as photons in discrete packets 1to1

39
Q

n. photons arriving per second=

A

rate / photon energy

40
Q

what is ke of electron further below the surface less than

A

hf - work function

41
Q

what will ke of emitted photons never be greater than

A

hf - work function

42
Q

how is validated evidence formed / what is it?

A

experiment/observation needs to be performed (to test a theory) (1) the results of (the experiment) need to be proved/repeatable/replicated/
confirmed (1)

43
Q

old theory is used to make what

A

predictions - then tested

44
Q

what is mercury vapour at low pressure

A

conducting

45
Q

ionisation energy

A

energy on level of ground state

46
Q

what’s ionisation

A

when an atom loses an orbiting electron (and becomes charged) (1)

47
Q

what happens to electrons in higher energy levels after a lower energy level electron is ionised

A

the orbiting electrons fall down (1)
to fill the vacancy in the lower levels (1) various routes down are possible (1) photons emitted (1)
taking away energy (1)

48
Q

in ionisation don’t say emitted say to

A

leave atom

49
Q

3 marker comparing ionisation and excitation for 1st say

A

in both electron receives exactly right amount of energy

50
Q

why can only photons of specific freq cause excitation in an atom

A

electrons occupy discrete energy levels
and need to absorb an exact amount of/enough energy to move to a higher level photons need to have certain frequency to provide this energy or e = hf
energy required is the same for a particular atom or have different energy levels all energy of photon absorbed
in 1 to 1 interaction or clear a/the photon and an/the electrons

51
Q

for line emission always say

A

how energy = wavelength equation and DIFF WAVELENGTHS PRODUCED ( as it is a spectrum)