Qustions on waves
1. circular arcs (penalise anything flat) B1
same constant wavelength before and after gap – judged by eye or labelled B1
this means at least 3 wavefronts need to be drawn
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2. for noticeable diffraction gap size (WTTE) B1
for sound much bigger than for light (WTTE) B1
[2]
3. (i) wave sources that have a constant phase difference (WTTE) B2
{max of 1 mark for sources have same frequency/wavelength/in phase C1}
(ii) sum of displacements (= resultant displacement) (WTTE) B1
(no marks for reference to amplitude)
[3]
4. (a) (i) constant phase difference
(allow 1 mark for same phase difference or same frequency/wavelength) B2
(ii) path difference = λ/2 B1
(b) (i) evidence shown that fringe width x = 8.0 mm B1
a = λD/x = 6.4 × 10–7 × 1.5/8.0 × 10–3 = 1.2 × 10–4 m C1
(give 2 marks for using x = 4.0 mm giving a = 2.4 × 10–4 m) A1
(ii) maximum intensity when y = 0 AND minima at +4 and –4 B1
correct repeat distance, i.e. 8.0 mm with at least 2 full cycles drawn B1
[8]
5. (i) semicircular wavefronts leaving the gap B1
no change in wavelength stated OR
clearly shown (at least 3 waves needed) – judged by eye B1
(ii) LESS diffraction would occur – shown or stated B1
wavefronts mainly plane (by eye) (allow curved at edges) B1
(iii) MORE diffraction for SOUND B1
Wavelength of sound > wavelength of light (WTTE) B1
Valid comparison of wavelength of light or sound with doorway e.g.
doorway of similar size to wavelength of sound OR
wavelength of light is very small compared to door (WTTE) B1
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6. (i) 1. path diff. = n (where n = 0,1,2 etc) {allow 0, OR , OR 2 etc} B1
2. path diff = (n ½) (where n = 0,1,etc) {allow = 0.5 OR,1.5, etc} B1
{do not allow answers purely about phase diff. e.g. with degrees or
used and no ref to }
(ii) recall of formula = ax/D C1
correct substitution for a, and D: e.g. = (4.86 10–7 2)/0.5 10–3 C1
x = 1.94 10–3 m (1.9 or 1.944) A1
(iii) central white fringe B1
other fringes are coloured (WTTE: e.g. allow spectrum formed) B1
[7]
7. diagram showing
laser/light source placed directly behind double slit AND screen placed
in front of slits B1
{single slit NOT required; no labelling required}
(i) D: allow any value between 30cm and 10m B1
(ii) a: allow any value between 0.1mm and 2mm B1
[3]
8. (a) (i) evidence of good practice: i.e distance for nx measured e.g.
5x = 18mm C1
x = 3.6 mm (OR 3.5 OR 3.7) A1
{x = 3.4, 3.8, 3.9, 4.0, or 4 mm, implying is directly
measured, and score 1 mark)
(ii) for O path difference = 0 B1
for A path difference = 3() B1
for B path difference = 1.5() B1
(b) recall of = ax/D OR =D/a OR B1
is smaller for blue light (than red light) hence is SMALLER (WTTE) B1
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9. Maximum of 2 marks for correctly identifying the 4 errors OR stating the 2
correct notes:
i.e. errors in notes 1, 2, 3, and 6 (shown anywhere) B2
{5 or 6 or 2 or 1 notes nominated scores ZERO, 4 correct scores 2, 3 correct scores 1}
Valid corrections score 1 mark each: do not allow “NOT” corrections apart
from note 3
Note 1: In longitudinal waves vibrations are parallel to wave direction (WTTE) B1
{OR in transverse waves vibrations are perpendicular to wave
direction (WTTE}
Note 2 light (or any of the em waves) can travel through a vacuum (WTTE) B1
{allow sound/longitudinal waves cannot travel thro’ a vacuum}
Note 3: waves carry energy/disturbance (not displacement or info)
from…. (WTTE) B1
{allow “waves do not carry the medium” and “the medium carries
the waves from…….”}
Note 6: wavelength = distance from crest to crest/trough to trough/max
to max (WTTE) B1
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