quantum

Question 1

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

Answer 1

• energy photon (1)

- greater than work function –so electrons emitted

Question 2

effect on current of increased intensity radiation (2)

Answer 2

• current greater (more electrons emitted per second)

- increased intensity = more photons incident per second

Question 3

work function

Answer 3

energy required to remove electron

minimum energy required to remove an electron from metal surface

Question 4

comparing x rays and UV - what can be said ?

Answer 4

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

Question 5

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

Answer 5

in current through photocell

Question 6

why emitted electrons have range kinetic energies up to a maximum

Answer 6

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

Question 7

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

Answer 7

-decrease energy photons
-decrease maximum kinetic energy electrons
-

Question 8

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

Answer 8

• increase photons - increase in emitted electrons

- double number electrons emitted per second

Question 9

why emitted electrons have range of ke to max 4

Answer 9

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

Question 10

what must happen to validate new scientific theory (2)

Answer 10

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

Question 11

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

Answer 11

surface attracts negative electron back to positive surface

photons have insufficient energy/energy required increased

Question 12

explain why ke emitted has max value

Answer 12

hf is energy available / recieved from photons

energy required to remove electron varies

Question 13

unit for work function

Answer 13

joules

Question 14

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

Answer 14

• work function minimum energy to release electron

- below certain frequency energy PHOTON less than work function

Question 15

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

Answer 15

photons as well as electrons

Question 16

when do E= hf its

Answer 16

in joules already

Question 17

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

Answer 17

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

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

Question 18

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

Answer 18

light travels in quanta / photon

old theory rejected

Question 19

state what is meant by threshold frequency

Answer 19

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

Question 20

always say in frequency questions

Answer 20

ENERGY PHOTON DEPENDS ON FREQUENCY

Question 21

why no photoelectric effect below threshold freq

Answer 21

(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)

Question 22

assumption in increase intensity increases current

Answer 22

one photon liberates one electrons - more photons incident per second

Question 23

2 points why a light causes photoelectric

Answer 23

high frequency above threshold

Question 24

for excitation say

Answer 24

up

Question 25

ionisation

Answer 25

electron removed from atom

Question 26

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

Answer 26

• 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)

Question 27

how are energy levels useful in explaining spectra (3)

Answer 27

• 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)

Question 28

for diffraction allowed size be within

Answer 28

same order magnitude (power of 10)

Question 29

piece of evidence for particle like properties

Answer 29

deflection in magnetic fields

Question 30

misconception on work function with electrons in metal

Answer 30

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

Question 31

always say in electron level negative explanation

Answer 31

WORK DONE to excite electrons

Question 32

must result in energy being emitted from atom =

Answer 32

relaxation

Question 33

when talking about photon absorption to move to higher level

Answer 33

ALL ENERGY ABSORBED IN 1TO1 INTERACTION

Question 34

electron can only trasnfer

Answer 34

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

Question 35

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

Answer 35

same number protons and neutrons

Question 36

what to say for diff maximum kinetic energy’s

Answer 36

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

Question 37

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

Answer 37

define it - minimum energy for electron to be liberated

Question 38

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

Answer 38

light travels as photons in discrete packets 1to1

Question 39

n. photons arriving per second=

Answer 39

rate / photon energy

Question 40

what is ke of electron further below the surface less than

Answer 40

hf - work function

Question 41

what will ke of emitted photons never be greater than

Answer 41

hf - work function

Question 42

how is validated evidence formed / what is it?

Answer 42

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

Question 43

old theory is used to make what

Answer 43

predictions - then tested

Question 44

what is mercury vapour at low pressure

Answer 44

conducting

Question 45

ionisation energy

Answer 45

energy on level of ground state

Question 46

what’s ionisation

Answer 46

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

Question 47

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

Answer 47

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)

Question 48

in ionisation don’t say emitted say to

Answer 48

leave atom

Question 49

3 marker comparing ionisation and excitation for 1st say

Answer 49

in both electron receives exactly right amount of energy

Question 50

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

Answer 50

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

Question 51

for line emission always say

Answer 51

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