Auckland Sports College

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Physics - Level 3 Waves

Immediately below this paragraph is a table with links to the exam questions and answers for all three externals way back to 2013. Focus on the exams for the last three years. Recognise the type of question e.g This is a question about..... Know how you are going to set out your working when answering each type of question.

Year

Waves

2025	Questions	Answers
2024	Questions	Answers
2023	Questions	Answers	Mr Whibley's video
2022	Questions	Answers	Mr Whibley's video
2021	Questions	Answers	Mr Whibley's video
2020	Questions	Answers	Mr Whibley's video
2019	Questions	Answers	Mr Whibley's video
2018	Questions	Answers	Mr Whibley's video
2017	Questions	Answers	Mr Whibley's video
2016	Questions	Answers
2015	Questions	Answers
2014	Questions	Answers
2013	Questions	Answers

We use the L3 Physics externals Scipad.   If you click on the resource booklet image a new window will open that shows you the formula sheet you will have in the exams.   We also use the free "College Physics" textbook from openstax

Waves

Mr Whibley has a helpful youtube video for this Level 3 Waves standard
 
But watch this video first
 

Waves - Standing Waves

These are discussed at 13:40 of theDrPhysicsA video
 
At Level 3 we are interested in stringed instruments like guitars (where there is a node at each end), open pipes (where there is an antinode at each end) and closed pipes (where there is a node at one end and an antinode at the other)
 
We are interested in the fundamental frequency (also called the first harmonic). This is the lowest frequency a standing wave can have. For a stringed instrument or an open pipe this is the frequency associated with half a wavelength. For a closed pipe this is the frequency associated with one quarter of a wavelength.
 
The second harmonic has twice the fundamental frequency. The third harmonic has three times the fundamental frequency, and so on.
 

 
Q1a from the 2023 exam

v=fλ
v = 196 x 2 x 0.331
v = 130ms^-2
Q1b from the 2023 exam

This is a merit question. it is easy


 

Waves - Doppler Effect

The Doppler effect is discussed at p59 of SciPad
 
Questions 1c and 1d from the 2023 exam actually explain the Doppler effect well when we use them as worked examples
 
Q1c from the 2023 exam



 
Q1d from the 2023 exam.

This is the excellence question

Waves - Beats

Q2a from the 2023 exam

The string is longer so the wavelength is longer. As v is unchanged and v = fλ , the fundamental frequency decreases.
 
Q2b from the 2023 exam

This is a merit question. it is easy

For Merit you need to describe the volume change and say in-phase is loud, out of phase is quiet
Beats are an example of interference. Constructive interference gives a loud beat. The frequency of a beat is the difference between the two frequencies. So, in this question if the violin string is out of tune and its first harmonic is 200Hz, the frequency of the beat will be 200-196 = 4 beats per second.
 
Question 2c from the 2023 Exam
Together, all four parts of this question make up an excellence question
 
Sam hear a beat of 2.1Hz
(i) Determine the possible frequencies at which the string is vibrating
 
Answer: 196 ± 2.1 = 193.9Hz or 198.1Hz
 
She increases the speed of the wave along the string by increasing the tension in the string and the beat frequency increases.
(ii) Use this information to determine the frequency at which the string was vibrating before adjustment.
 
Answer: The length of the string has not changed (i.e the wavelength is the same) so the increase in the speed of the wave means frequency has increased. The increase in beat frequency tells us that the string is vibrating further from 196 Hz, so the string must have been at 198.1 Hz.
 
(iii) Explain what Sam must do to get the string to vibrate at 196 Hz
 
Answer: Sam must decrease the tension to get the string to 196 Hz. (decrease v to lower f).
 
(iv) State how she will know when the string is vibrating at 196 Hz.
 
Answer:When the string is vibrating at exactly 196 Hz, there is no beat. She will hear a steady 196 Hz tone.
 
Q2d from the 2023 exam
This is another excellence question


 
Watch this youtube video about the natural frequency of a system/object, forced oscillations, and resonance
 
Resonance occurs when the driving frequency is equal to the natural frequency.

Waves - Interference Patterns and Diffraction

Interference is discussed at 12:08 of theDrPhysicsA video
 
Watch this youtube video for an example of interference patterns in ripples from a pond
 
Find some time to watch this video as well
 
And watch this youtube video for a demonstration of the interference patterns from Young's double slit experiment
 
Diffraction is the spreading out of waves when they pass through a gap
 
For your exam there is one triangle you need to know in order to work out either θ or the distance between the central antinode and another antinode or node. This has one side (the adjacent) which is the distance from the 'gap' or source to the screen. It has length 'L'. The distance 'x' from the central antinode to whichever other antinode you are interested in is the 'opposite' side and tanθ is L/x. So you can work out θ if you know 'L' and 'x' and you can work out 'x' if you know 'L' and θ. You will probably need to work out θ so you can use it in the formula nλ = dsinθ
 

 

 
If 'x' is a lot smaller than 'L' (as happens when there are only 2-slits or two sources) then θ is small and sinθ ≈ tanθ, so you can use x/L as an approximation for sinθ
 
With the diffraction grating the antinodes are further apart so 'x' is larger and the approximation sinθ ≈ x/L cannot be used.
 
Diffraction is discussed at 18:20 of theDrPhysicsA video
 
Watch this youtube video about the diffraction gratings
 

Q3a from the 2023 exam

 
Answer: Diffraction is the spreading out of waves as they go through a gap (or bend around an obstacle).
 
Q3b from the 2023 exam
This is another excellence question

Answer: Waves from multiple slits overlap and superpose. If the waves didn’t spread out, they wouldn’t overlap and interfere.
The waves only arrive in phase and reinforce at the places where the path difference from successive slits is a whole number of wavelengths (nλ). The light is bright in these places.
When n is not a whole number, even if the phase difference, θ , between two adjacent slits is small, then the phase difference between subsequent slits will be increasing multiples of θ.
With many sources there will be waves from different slits arriving in antiphase and the overall interference will cause many more points of destructive interference resulting in a wide dark region between the bright fringes
 
2023 Exam Question 3c
 
3c. Calculate the slit separation in the grating.
 

 
Q3d from the 2023 exam