2822/01 Physics A: Electrons and Photons. June Mark Scheme

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1 2822/01 Physics A: Electrons and Photons June 2004 Mark Scheme

2 The following annotations may be used when marking: X = incorrect response (errors may also be underlined) ^ = omission mark bod = benefit of the doubt (where professional judgement has been used) ecf = error carried forward (in consequential marking) con = contradiction (in cases where candidates contradict themselves in the same response) sf = error in the number of significant figures Abbreviations, annotations and conventions used in the Mark Scheme: / = alternative and acceptable answers for the same marking point ; = separates marking points NOT = answers not worthy of credit ( ) = words which are not essential to gain credit (underlining) = key words which must be used ecf = allow error carried forward in consequential marking AW = alternative wording ora = or reverse argument

3 CATEGORISATION OF MARKS The marking schemes categorise marks on the MACB scheme. B marks: M marks: C marks: A marks: These are awarded as independent marks, which do not depend on other marks. For a B-mark to be scored, the point to which it refers must be seen specifically in the candidate s answers. These are method marks upon which A-marks (accuracy marks) later depend. For an M-mark to be scored, the point to which it refers must be seen in the candidate s answers. If a candidate fails to score a particular M-mark, then none of the dependent A-marks can be scored. These are compensatory method marks which can be scored even if the points to which they refer are not written down by the candidate, providing subsequent working gives evidence that they must have known it. For example, if an equation carries a C- mark and the candidate does not write down the actual equation but does correct working which shows the candidate knew the equation, then the C-mark is given. These are accuracy or answer marks, which either depend on an M-mark, or allow a C-mark to be scored.

4 to 10-1 (m) (Allow range: m to 0.15 m) (b) (c) Any one from: 1. Travels at the speed of light / (ms -1 in vacuum) 2. Travel in vacuum (Allow free space but not just space ) 3. Transverse (wave) / can be polarised 4. Consists of oscillating electric and magnetic fields 5. Can be reflected / refracted / diffracted / shows interference 6. (Behave as) photon(s) 7. Warms food W 78 (e.m.f. =) / (e.m.f. =) Q 24 (e.m.f. =) (V) [Total: 4] 2 (b) Energy (transformed by a device working) at 1 kw for 1 hour E = Pt / 5.8 = 0.12 time / (time =) 48.3 (hr) (time =) (s) [Total: 3] 1

5 3 (b)(i) Line crosses y-axis at 1.4 (V) / V = E or 1.4(V) when I = 0 V = E Ir; since I = 0 (Hence V = E or 1.4(V) ) (Graph extrapolated to give) current = 2.0 (A) (Allow tolerance ± 0.1A) (b)(ii) (b)(iii) E = I (max) r gradient = r (Ignore sign) 1.4 (r = ) 2.0 (Attempt made to find gradient) r = 0.7(0) (Ω) r = 0.7(0) (Ω) (Possible ecf) (excessive) heating of cell / energy wasted internally / cell might explode / cell goes flat (quickly) [Total: 5] 2

6 4 (b)(i) (b)(ii)1. (b)(ii)2. Correct circuit for both lamps in parallel (ignore ammeter here) Ammeter placed correctly in series with P The resistance of LDR/circuit changes (as light intensity changes) When blade blocks light, resistance of LDR/circuit is large(r) (ora) Correct statement about p.d (Possible ecf) (V = ) 2.0 (V) (Allow 1 sf answer) R2 V = V0 I = 2.0/2200 / (A) R1 + R2 R (3.0 = 0 R ) (R = 3.0 / ) R = 3300 (Ω) R = 3300 (Ω) Possible ecf (For V LDR = 2.0 V, R = 1.47 kω. This scores 1/2) (If 3.5 V given in (b)(ii)1., then R = 940 Ω. This scores 2/2) [Total: 8] 3

7 5 (resistance = ) p.d./current (Allow use of voltage ) B2 ((resistance =) ratio of p.d. to current 2/2) ((resistance =) voltage per (unit) current 2/2) ((R = ) V/I scores 1/2) ((resistance =) voltage per (unit) ampere scores 1/2) (b)(i) (b)(ii)1. (b)(ii)2. (b)(ii)3. Parallel = + R R R / 1 3 = R 18 (R =) 6.0 (Ω) (Allow 1 sf answer) 2 V P = (Allow P = VI or P =I 2 R) R 12 2 ( P = ) 6 P = 24 (W) (Possible ecf from (b)(ii)1.) (If 18 Ω used, P = 8 (W). Allow 1/2) R = ρl (Allow other subject) A = A A = (m 2 ) ( (m 2 ) scores 2/3) (If R = 6.0 Ω then A = (m 2 ). This scores 2/3) [Total: 10] 4

8 6 Arrow towards the cloud (b) Into the page (No ecf from ) (c)(i)1. (c)(i)2. (c)(ii) ΔQ I = (Allow other subject, with or without Δ) Δt (charge =) (C) (Ignore minus sign) ( (C) scores 2/3) (number =) (Possible ecf) e (number =) F = BIL (F =) (F =) ( scores 2/3) newton / N / TAm / Jm -1 [Total: 11] 5

9 7 Any five from: 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 = φ + KE (max) (b)(i)1. (b)(i)2. (b)(ii) (c) [QWC: Spelling and Grammar] (energy of photon = ) 2.5 (ev) (energy =) (Possible ecf from (b)(i)1.) (J) (Allow 1 sf answer) (f =) (Possible ecf) h (f = ) (f =) (Hz) (Allow ) Each photon has more energy / There are fewer photons (in a given time because intensity is the same) Smaller current [Total: 13] 6

10 8 Any five from: 1. Electrons travel / move as a wave 2. Electrons show diffraction / interference (effects) 3. Diffraction (is noticeable) when λ comparable to gap size 4. Mention of de Broglie equation: λ = h mv 5. λ, h, m and v correctly identified in 4. above 6. Graphite / matter / atoms / nuclei / small gap(s) needed to diffract electrons 7. Experimental evidence: (diffraction) rings / fringes (Can score on a diagram) 5 [QWC: Organisation] [Total: 6] 7

2822 Electrons and Photons. June Mark Scheme

2822 Electrons and Photons. June Mark Scheme 2822 Electrons and Photons June 2003 Mark Scheme Categorisation of marks The mark scheme categorises marks on the MACB scheme. B marks: These are awarded as independent marks, which do not depend on other