AQA A Level Physics
AQA A Level Physics 3.3 Waves and Periodic Motion Exam Questions
Free AQA A Level Physics exam questions for 3.3 Waves and Periodic Motion, with a mark scheme for every pack. Covers progressive and stationary waves, polarisation, interference, diffraction, refraction, optical fibres, circular motion and simple harmonic motion.
3.3 Waves and Periodic Motion exam questions
1 question pack of real past exam questions, each with its mark scheme. Do not stop after a few: answer as many as you can without notes, then mark every answer with the mark scheme. The more questions you do, the more quickly you will spot how examiners ask about each idea.
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About AQA A Level Physics 3.3 Waves and Periodic Motion
This topic brings together AQA section 3.3 Waves and the periodic motion content from section 3.6.1 (circular motion and simple harmonic motion), all of which is examined on Paper 1. In waves you study progressive waves, longitudinal and transverse waves, polarisation, stationary waves, path difference and coherence, Young's double slit, diffraction gratings, refraction and total internal reflection in optical fibres. Periodic motion adds angular speed, centripetal force, SHM equations, mass-spring and simple pendulum systems, energy in SHM and resonance. Examiners regularly test required practicals such as stationary waves on a string, Young's slits or gratings and the SHM practical, so know methods as well as equations.
What you need to know
- Progressive waves Know amplitude, frequency, wavelength, speed, phase and phase difference (in degrees or radians). Use c = f lambda and f = 1/T. Polarisation only happens with transverse waves and is used in Polaroid sunglasses and aerial alignment.
- Stationary waves Formed by superposition of two waves of the same frequency travelling in opposite directions. Nodes are 1/2 wavelength apart. For the first harmonic on a string f = (1/2L) x square root of (T/mu). This is a required practical.
- Interference and diffraction Coherent sources have a constant phase difference and the same frequency. Young's slits: fringe spacing w = lambda D / s. Diffraction grating: d sin theta = n lambda. Laser safety must be described in practical answers.
- Refraction and optical fibres Refractive index n = c/cs. Snell's law n1 sin theta1 = n2 sin theta2. Critical angle sin thetac = n2/n1. Cladding protects the core and reduces modal dispersion; know material dispersion and absorption.
- Circular motion Angular speed omega = v/r = 2 pi f. Centripetal acceleration a = v^2/r = omega^2 r, and centripetal force F = mv^2/r. The force acts towards the centre and does no work.
- Simple harmonic motion Defined by a proportional to minus x. Use x = A cos omega t, v = plus or minus omega square root of (A^2 - x^2), a(max) = omega^2 A. Mass-spring: T = 2 pi square root of (m/k); pendulum: T = 2 pi square root of (l/g) for small angles.
- Energy and resonance In SHM energy transfers between kinetic and potential, total constant if undamped. Forced vibrations at the natural frequency give resonance; damping lowers the peak amplitude and broadens it.
Common mistakes in 3.3 Waves and Periodic Motion
- Saying nodes are one wavelength apart. Adjacent nodes are half a wavelength apart.
- Writing that diffraction makes waves change speed. Diffraction is spreading through a gap or round an edge; the speed and wavelength stay the same.
- Using degrees in SHM equations with the calculator in the wrong mode. In x = A cos omega t the angle is in radians.
- Describing centripetal force as an extra outward force. It is the resultant force towards the centre, provided by tension, gravity, friction or another real force.
- Giving the maximum order of a grating by rounding d/lambda up. The maximum order is the whole number below d/lambda because sin theta cannot exceed 1.
Try three 3.3 Waves and Periodic Motion exam-style questions
1. A 0.40 kg mass on a spring of stiffness 25 N m-1 oscillates with amplitude 0.050 m. Calculate the period and the maximum speed. (4 marks)
Show the mark scheme answer
T = 2 pi square root of (0.40/25) = 2 pi x 0.126 = 0.79 s; omega = 2 pi/T = 7.9 rad s-1 (or square root of k/m); v(max) = omega A = 7.9 x 0.050; = 0.40 m s-1 (0.395).
2. Light of wavelength 600 nm is incident on a grating with 300 lines per mm. Calculate the angle of the first order maximum and the highest order visible. (4 marks)
Show the mark scheme answer
d = 1/300000 = 3.33 x 10^-6 m; sin theta = lambda/d = 6.0 x 10^-7 / 3.33 x 10^-6 = 0.18 so theta = 10.4 degrees; d/lambda = 5.6; highest order is 5.
3. Explain how a stationary wave forms on a string fixed at both ends. (3 marks)
Show the mark scheme answer
Waves reflect at the fixed ends; the reflected and incident waves have the same frequency and travel in opposite directions; they superpose; nodes form where they are always in antiphase and antinodes where they are in phase, at frequencies where a whole number of half wavelengths fit the string.
3.3 Waves and Periodic Motion FAQs
What does AQA A Level Physics Waves and Periodic Motion cover?
It covers progressive and stationary waves, polarisation, interference, diffraction, refraction and optical fibres, plus circular motion and simple harmonic motion including resonance and damping.
Which paper is waves and periodic motion examined in?
Sections 3.3 and 3.6.1 are both assessed on Paper 1, and the required practicals linked to them can also appear on Paper 3.
Which required practicals link to this topic?
The stationary waves on a string practical, the Young's slits and diffraction grating practical, and the SHM practical (mass-spring or pendulum) all belong here. Learn the method, the graph you would plot and how to reduce uncertainty.
