Y12 Questions on Photons
1. 3.9 eV = 3.9 × 1.6 × 10–19 J (= 6.24 × 10–19 J) (1)
λ = hc/E = 6.63 × 10–34 × 3.0 × 108 / 3.9 × 1.6 × 10–19 (= 320 × 10–9 m) (1) 2
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2. (i) 1. E = hf / / f = 7.5 1017 (Hz) C1
(‘E = hf’ can be secured in (i))
/ E = 6.63 10–34 7.5 1017 C1
energy = 4.97 10–16 (J) 5.0 10–16 (J) (Allow 1 sf answer here) A1
2. (Possible ecf)
energy = 3.1 103 (eV) B1
(ii) The answer to (c)(i)1. and 1.4 (W) are used to determine the rate
of photons C1
(Possible ecf) C1
number = 2.8 1015 (s–1) (If 3100 eV is used, then allow 2/3 for 4.5 10–4) A1
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3. (Allow any subject) C1
C1
v = 1.43 103 1.4 103 (ms–1) A1
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4. (i) Visible (light) B1
(ii) work function = 1.9 1.6 10–19 M1
work function = 3.04 10–19 (J) 3.0 10–19 (J) A0
(iii) 1. E = hf / C1
E =
E = 3.9 10–19 (J) A1
2. hf = + KE(max) / hf = + ½ mv2
(Allow E = + ½ mv2 if E is qualified in (iii)1.) C1
3.9 10–19 = 3.0 10–19 + KE(max) / 3.9 10–19 = 3.04 10–19 + KE(max) C1
KE = 9.0 10–20 (J) / KE = 8.6 10–20 (J) (Possible ecf) A1
(iv) No change (to maximum KE of electron) B1
Each photon has same energy (but there are fewer photons) B1
(v) number of photons = ( 2.05 1017) (Possible ecf) C1
number of electrons = 0.07
number of electrons = 1.44 1016 (s–1) 1.4 × 1016 (s–1) A1
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5.
(Four correct: 3 marks, three correct: 2 marks, two correct: 1 mark) B3
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6. (i) particle / particulate / quantum / photon B1
(ii) wave B1
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7. Maximum of three from points 1 to 6: B1 3
1. Photon mentioned (e.g.: photons interact with the surface electrons)
2. Energy is conserved (between the photon and the electron / in the interaction)
3. hf = KE(max)
4. A single photon interacts with a single electron / It is a one-to-one interaction
5. Electron is removed when photon energy is greater than / equal to the
work function
(energy) / (Allow ora)
6. Electron removed when frequency is greater than / equal to the threshold
frequency (Allow ora)
7. (Visible) light has lower frequency than the threshold frequency / Energy of
(visible) light photon is less than the work function (energy) (ora with uv) B1
8. Greater intensity of (visible) light means more photons (per unit time) /
energy of a photon remains the same B1
QWC Spelling, punctuation and grammar B1
Organisation B1
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8. (a) quantum of energy / radiation / packet of energy B1
(b) (i) f = E/h = 5.60 × 10–19 /6.63 × 10–34 C1
f = 8.45 × 1014 (Hz) A1
(ii) 1 minimum energy to release an electron from the surface (of the metal) B1
2 5.60 × 10–19 – 4.80 × 10–19 ( = 8.0 × 10–20 J) B1
(iii) 8.0 × 10–20 = ½(9.1 × 10–31)v2 M1
giving v = 4.2 × 105 (m s–1) A1
(c) (i) Correct selection of: λ = h/p or λ = h/mv M1
where all symbols are defined A1
(ii) λ = 6.6 × 10–34 /(9.1 × 10–31 × 4.2 × 105) C1
λ = 1.7 × 10–9 (m) A1
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9. (a) one (or more) electrons removed (or added) to an atom 1
(b) E = hf = hc/λ together with knowledge of symbol meaning (1)
= (1)
= 8.36 × 10–19 (J) (1) 3
(c) frequency of UV is greater than frequency of light
OR alternative statement in terms of wavelength.
so photon energy of visible light is less than photon energy of UV (1)
PLUS one of the idea of conservation of energy
it is not possible for a low energy photon to give a high energy photon
this is a one to one process (1) 2
(d) E = V/d and power of 10 correct for d (1)
= 30/0.00020 = 150 000 (1)
V m–1 (1) 3
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10. (a) Maximum of five marks
Up to four from:
/ M1
All symbols (, h, m and v or p) defined A1
Electrons travel / move / propagate (through space) as a wave B1
Electrons are diffracted / ‘spread out’ M1
by the atoms / spacing between the atoms A1
The electrons are diffracted when their wavelength is less than or
comparable or same as size of atoms / gap between the atoms B1
Up to two from:
When the speed of electrons is increased) the rings ‘get smaller’ B1
(At greater speed of electrons) the wavelength is shorter B1
(At greater speed of electrons) there is less diffraction B1
QWC Organisation B1
Spelling, punctuation & grammar B1
(b) Electrons have mass / momentum / charge / can be ‘accelerated’ B1
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11. (i) The minimum frequency needed to free an electron
(from the surface of a metal) B1
(ii)1 Line extended intersects (the f axis at) this value / At this frequency, Ek = 0 B1
(ii)2 ( = ) h 5.0 1014 / ( = ) 6.63 10–34 5.0 1014 C1
work function energy = 3.3 10–19 J A1
(iii)1 1 The gradient / slope of the line is the same B1
The gradient is equal to h / independent of the metal B1
(iii)2 The line is shifted to the right B1
The threshold frequency is greater (AW) B1
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12. (a) Any five from: B1 × 5
1. Photoelectric (effect) mentioned
2. Photon(s) mentioned in correct context / E = hf
3. One-to-one ‘interaction’ between photon & electron
4. Surface electrons are involved
5. Electron released / photoelectric (effect) when photon
energy > / = work function (energy)
6. Electrons emitted / photoelectric (effect) when
frequency > / = threshold frequency
7. Energy is conserved (in the ‘interaction’ between photon and electron)
8. Reference to Einstein’s equation: hf = + KE(max)
[QWC: Spelling and Grammar]
(b) (i) 1. (energy of photon = 2.2 + 0.3) B1
2.5 (eV) B1
2. (energy =) 2.5 1.6 10–19 (Possible ecf from (b)(i)1.) C1
4.0 10–19 (J) (Allow 1 sf answer) A1
(ii) (f =) (Possible ecf) C1
(f = )
(f =) 6.03 1014 6.0 1014 (Hz) (Allow 6 1014) A1
(c) Each photon has more energy / There are fewer photons (in B1
a given time because intensity is the same)
Smaller current B1
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13. (i) 1. The minimum frequency (of radiation \ waves) needed for electrons
to be released (from the metal surface) \ for photoelectric effect B1
2. Its temperature increases \ gets warm \ ‘heats up’ B1
(ii) E = 2.2 1.9 (= 4.1) C1
E = 4.1 1.6 10–19 = 6.56 10–19(J) C1
(Allow this mark for correct conversion of either 1.9 eV or 2.2 eV to joules)
C1
= 3.03 10–7 3.0 10–7(m)
(Allow 1 sf answer) A1
(Allow 3/4 marks for = 4.85 10–26 m when eV is not converted to joules)
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