Waves flashcards

Waves transfer energy without transferring matter. Students must understand the difference between transverse and longitudinal waves, and be able to define key quantities: amplitude, frequency, wavelength, period and wave speed, linked by v = f x wavelength and T = 1/f. The behaviour of waves includes reflection, refraction, diffraction and superposition. Superposition leads to interference, which can be constructive or destructive depending on path difference and phase difference. Students must understand standing waves, including the formation of nodes and antinodes, and be able to identify harmonics on strings and in pipes. The Doppler effect describes how observed frequency changes when a source or observer moves. Sound and light both exhibit wave behaviour, and understanding polarisation confirms that light is a transverse wave.

1. Card 1

   What is the difference between a transverse and a longitudinal wave?

   In a transverse wave the oscillation is perpendicular to energy transfer; in a longitudinal wave the oscillation is parallel to the direction of energy transfer.

2. Card 2

   Define the amplitude of a wave.

   Amplitude is the maximum displacement of a particle from its equilibrium position, measured in metres.

3. Card 3

   State the wave speed equation linking v, f and wavelength.

   Wave speed v = f x wavelength, where f is frequency in Hz and wavelength is in metres, giving v in metres per second.

4. Card 4

   What is the relationship between period T and frequency f?

   Period T = 1/f. Period is the time for one complete oscillation; frequency is the number of oscillations per second, measured in hertz.

5. Card 5

   State the principle of superposition.

   The principle of superposition states that when two waves meet, the resultant displacement equals the vector sum of the individual displacements at that point.

6. Card 6

   What conditions produce constructive and destructive interference?

   Constructive interference occurs when path difference = n x wavelength (in phase); destructive interference occurs when path difference = (n + 0.5) x wavelength (antiphase).

7. Card 7

   What is a standing wave and how does it form?

   A standing wave forms when two identical waves travel in opposite directions and superpose, creating fixed nodes (zero displacement) and antinodes (maximum displacement).

8. Card 8

   What is the wavelength of the fundamental mode on a string of length L fixed at both ends?

   For the fundamental mode (first harmonic) on a fixed string, wavelength = 2L, so the string length equals exactly half a wavelength.

9. Card 9

   Explain what diffraction is and when it is most significant.

   Diffraction is the spreading of a wave as it passes through a gap or around an obstacle; it is greatest when the gap width is approximately equal to the wavelength.

10. Card 10

    What does it mean for two waves to be coherent?

    Coherent waves have a constant phase difference and the same frequency, which is necessary to produce a stable interference pattern.

11. Card 11

    Describe the Doppler effect for a moving sound source.

    The Doppler effect is the change in observed frequency when source and observer move relative to each other; a source approaching gives a higher observed frequency.

12. Card 12

    Why does polarisation demonstrate that light is a transverse wave?

    Polarisation restricts oscillations to one plane; only transverse waves can be polarised, confirming light oscillates perpendicular to its direction of travel.

• Students often confuse the wave speed with the speed of individual particles in the medium, forgetting that wave speed depends on the medium while particle speed depends on amplitude and frequency.
• A common error is assuming that a path difference of one full wavelength causes destructive interference, when in fact it causes constructive interference because the waves are back in phase.
• Many students incorrectly apply the standing wave formula by forgetting that an open end of a pipe is an antinode and a closed end is a node, leading to wrong harmonic wavelengths for open and closed pipes.

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