12 Waves 2 Exam-style mark scheme

OCR Physics A

Question Answer Marks Guidance

1

B1

2 a Constant phase relationship (and same frequency) B1 Allow: constant phase difference

2 b i For waves A and B:

T = 3 ms

Hz3.3331==

Tf

fv

=λ

λ = 0.99 m

Both waves have the same frequency and wavelength

M1

M1

A1

B1

This mark is independent

2 b ii t = 0 ms

resultant = +5

t = 4.5 ms

resultant = –5

B1

B1

Plus and minus signs needed for both

2 c Phase difference =

2π

Delay wave B by 41 × 3 = 0.75 ms

or

Delay wave A by 45 × 3 = 3.75 ms

M1

A1

This mark can be awarded for answers in terms of wavelength instead of T

2 d Correct phase difference, one wave delayed by

43λ

Same wavelength

One wave should have twice the amplitude of the other

B1

B1

B1

Only award if x-axis labelled with ‘distance’

© Oxford University Press 2015 www.oxfordsecondary.co.uk/acknowledgements

This resource sheet may have been changed from the original 1

12 Waves 2 Exam-style mark scheme

OCR Physics A

Question Answer Marks Guidance

3 a i Connect to the same signal generator

Ensure same polarity in wires

B1

B1

3 a ii High amplitude in the centre

Alternating high/low amplitude regions

All sections of high and low amplitude equi-width

B1

B1

B1

Allow: a correct diagram for all three marks, same as marking points on the left

3 a iii Accept one mark maximum:

• lower amplitude at all points

• high/low sections spaced further apart

B1 ×1

3 b i To diffract the laser light (to ensure two coherent sources from double slit)

B1

3 b ii x =

9105.8 3–×

= 9.44 × 10–4

λ = 8.2

1044.9102 43 −− ×××

λ = 6.7 × 10–7 m

M1

M1

A1

Need to recognise that 10 fringes means nine fringe spacings.

3 b iii No effect B1

3 c Brighter fringes

Fringes further spaced / fringes very narrow

B1

B1

Same marking point

4 a Node and antinode must be labelled. B1 Both required for mark

4 b 57 mm B1 Tolerance ±1 mm

4 c Any two points between two nodes (or two points on every other loop).

Anywhere on loop above for example.

B1

4 d λ = 0.3 m

v = f × λ

v = 150 × 0.3 = 45 m s–1

M1

A1

4 e i Phase difference:

B = 0 or 2π; C = π; D = 0 or 2π

Displacement:

A = 10 mm; B = 5 mm; C = 10 mm; D = 10 mm

B1

B1

All three needed for mark

All four needed for mark

4 e ii T =

f1 =

2501 = 4 × 10–3 s

1 ms = 41 of a complete oscillation

Flat horizontal line

M1

M1

A1

© Oxford University Press 2015 www.oxfordsecondary.co.uk/acknowledgements

This resource sheet may have been changed from the original 2

12 Waves 2 Exam-style mark scheme

OCR Physics A

Question Answer Marks Guidance

5 a

λ = 32 of the wave = 0.4 m

f = 3 × f0

f = 768 Hz

B1

B1

B1

Possible e.c.f.

5 b i

λ = 4 × 2.5 = 10 cm

M1

A1

Possible e.c.f.

5 b ii Resonance achieved at second harmonic, which is

43 of

a complete wave

Length = 3 × 25 = 75 cm

M1

A1

Allow: diagram for M1 mark

Unit required for mark

5 c i One mark for each correct diagram

B1 ×3 Each diagram must be labelled correctly with the harmonic

5 c ii 1st harmonic λ = 2L; f0 =

Lv2

2nd harmonic λ = L; f1 = Lv or = 2f0

3rd harmonic λ = 32L ; f2 =

Lv

23 or = 3f0

B1

B1

B1

Must have wavelength and frequency for each B1 mark

© Oxford University Press 2015 www.oxfordsecondary.co.uk/acknowledgements

This resource sheet may have been changed from the original 3