AS Physics: Waves and Superpositions

Common Past paper questions

By reference to the direction of transfer of energy, state what is meant by longitudinal waves?

Oscillations (of particles) are parallel to (the direction) of energy transfer.

Define frequency of a wave sound.

Frequency is the number of vibrations/oscillations per unit time or the number of wavefronts passing a point per unit time.

A sound wave travels through air. Describe the motion of the air particles relative to the direction of travel of the sound wave.

vibrations/oscillation of the air particles are parallel to the direction of it (the direction of travel of the sound wave).

Describe Doppler Effect.

Observed frequency is different to source frequency when source moves relative to observer.

State what is meant by the frequency of a progressive wave.

The number of oscillations per unit time.

By reference to the direction of the propagation of energy, state what is meant by a longitudinal wave.

vibrations/oscillations (of the particles/wave) are parallel to the direction OR

in the same direction (of the propagation of energy)

By reference to the direction of the propagation of energy, state what is meant by a transverse wave.

vibrations/oscillations (of the particles/wave) are perpendicular to the direction (of propagation of energy)

Describe Doppler effect

change/difference in the __observed/apparen__t frequency when the source is moving (relative to the observer).

A progressive wave transfers energy. A stationary wave does not transfer energy. State two other differences between progressive waves and stationary waves.

• Progressive waves - travel through a medium.

• Stationary waves - while stationary waves do not travel.

• Progressive waves all particles have same amplitude.

• Stationary waves - no nodes or antinodes or maximum to minimum/zero amplitude.

• Progressive waves - adjacent particles are not in phase.

• Stationary waves - waves particles are in phase (between adjacent nodes).

What is meant by progressive wave.

energy is moved/transferred/propagated from one place to another (without the bulk movement of the medium).

What is meant by transverse wave.

(particles) oscillate/vibrate at right angles to the direction of travel of the energy/ wavefront.

Define frequency.

number of oscillations per unit time/ number of wavefronts passing a point per unit time.

State what is meant by zero phase difference.

two sound waves of the same frequency that are perfectly aligned have a phase difference of 0 and are said to be “in phase.”

two waves that are in phase add to produce a sound wave with an amplitude equal to the sum of the amplitudes of the two waves.

Explain what is meant by the following quantities for a wave on the surface of water.

i) displacement

ii) amplitude

iii) frequency

iv) time period

i) displacement - distance from the equilibrium position/ undisturbed position/ midpoint/ rest position

ii) amplitude - is the maximum displacement

iii) frequency - is the number of wavefronts/ crests passing on a point per unit time

iv) time period - is the time between adjacent wave fronts

Explain the term displacement for the wave on the rope.

the distance the rope/ particles are (above or below) from the equilibrium/ mean/ rest/ undisturbed position (NOT distance moved)

Define for a wave:

i) wavelength λ

ii) frequency f

i) wavelength - minimum distance between two points moving in phase OR distance between neighbouring or consecutive peaks or troughs OR wavelength is the distance moved by a wavefront in time T or one oscillation/cycle or period (of source)

ii) frequency - number of wavefronts/ (unit) time OR number of oscillations per unit time or oscillations/time

Use your definitions (in flashcard 16) to deduce the relationship between λ, f and speed v of the wave.

State one property of electromagnetic waves that is not common to other transverse waves.

travel through vacuum/ free space

All the waves in a spectrum can be polarised. Explain the meaning of the term polarised.

vibrations are in one direction perpendicular to direction of propagation/ energy transfer

A polarised wave oscillates in only one plane (e.g only up and down if vertically polarised), only transverse waves can be polarised. Polarisation provides evidence for the nature of transverse waves because polarisation can only occur if a wave's oscillations are perpendicular to its direction of travel (as they are in transverse waves).

The intensity of a wave is affected by polarisation. As the process of passing through a polarising filter excludes waves of certain orientations, the intensity of the wave after filtering is always less than or equal to its intensity before.

Explain the following terms used to describe stationary waves on a string:

i) node

ii) antinode

i) node - zero amplitude/displacement

ii) antinode - maximum amplitude/displacement

A loudspeaker produces a sound wave of constant frequency. Outline how a cathode ray oscilloscope (c.r.o) can be used to determine this frequency.

connect microphone / (terminals of) loudspeaker to Y-plates of c.r.o. adjust c.r.o. to produce steady wave of 1 (or 2) cycles / wavelengths on screen

measure length of cycle / wavelength and note time-base b

frequency= 1/λb

(assume b is measured as s cm^-1 unless otherwise stated)

(if statement is 'measure T, f= 1/T’ then last two marks are lost)

For a progressive wave, state what is meant by its meant by its period.

time for one oscillations/vibrations/cycle OR time between a__djacent__ wavefronts (passing the same point) OR shortest time between two wavefronts (passing the same point)

State the principle of superposition.

(when two or more) waves meet/overlap (at a point)

(resultant) displacement is sum of the individual displacements

What is meant by a node of a stationary wave.

particle on stationary wave with zero amplitude.

Difference between nodes vs antinodes.

State what is meant by coherent in a wave.

constant phase difference in a wave.