Retrieval Practice
Wave Types, Polarisation & Stationary Waves — AQA A-Level Physics
Q1. Define a transverse wave and give two examples.
- A wave where particles oscillate perpendicular to the direction of wave travel.
- Examples: visible light (EM wave), waves on a string.
Q2. Define a longitudinal wave and give two examples.
- A wave where particles oscillate parallel to the direction of wave travel.
- Examples: sound waves, seismic P-waves.
Q3. Why can longitudinal waves not be polarised?
- They oscillate parallel to the direction of travel, so there is only one plane of oscillation.
- Polarisation requires restricting oscillations to one of many possible planes.
Q4. State what polarisation is.
When particle oscillations occur in only one direction perpendicular to the direction of wave propagation.
Q5. Explain how polaroid sunglasses reduce glare from water.
- Light reflected from water is partially horizontally polarised.
- Polaroid lenses have vertical transmission axes, so they block the horizontally polarised glare.
Q6. State the principle of superposition.
When two or more waves overlap at a point, the resultant displacement equals the sum of the individual displacements.
Q7. How is a stationary wave formed?
- Two waves of the same frequency and amplitude travel in opposite directions and superpose.
- Usually a wave and its reflection.
Q8. Define a node and an antinode.
- Node: a point of zero displacement at all times.
- Antinode: a point of maximum amplitude.
Q9. State the wavelength and frequency of the first harmonic on a string of length L.
- Wavelength = 2L.
- Frequency f1 = v / (2L).
Q10. What is the relationship between the nth harmonic frequency and the fundamental?
- f_n = n x f_1.
- Each harmonic is an integer multiple of the fundamental.
Q11. State the equation for the first harmonic frequency in terms of tension and mass per unit length.
f = (1 / 2L) x sqrt(T / mu), where T is tension (N) and mu is mass per unit length (kg/m).
Q12. In the required practical for stationary waves, what do you plot and what does the gradient give?
- Plot f against 1/L.
- Gradient = v/2, so wave speed = 2 x gradient.