19. Wave sources are coherent when they produce waves of the same frequency that are either in phase or a constant phase difference apart.
20. Waves are ‘in phase’ when the crests from one source meet crests from another.
21. Destructive interference is when two or more waves combine, resulting in a single wave of smaller amplitude than the source waves.
22. Waves are ‘out of phase’ when the crests from one source meet the troughs from another.
23. An interference pattern is the pattern formed when waves from two (or more) coherent sources combine; it contains a repeating pattern of constructive and destructive interference.
24. Polarisation is when the direction of vibration of a wave is restricted to one plane.
Sound 1. Sound is a form of energy that travels by longitudinal mechanical waves. 2. Natural frequency is the frequency that a body oscillates at when vibrating freely.
3. Resonance is the rapid amplification of oscillation when a periodic force is applied at the same frequency as the natural frequency of the body.
4. A stationary wave is a wave that remains in a constant position; it is made up of a series of nodes and antinodes.
5. Nodes are the points where there is no vibration. 6. Antinodes are the points where there is maximum vibration. 7. Fundamental frequency is the lowest natural frequency of a vibrating object. 8. Harmonics are multiples of the fundamental frequency.
9. The ‘quality’ of a note describes the shape of the sound wave; it depends on the number and amplitudes of the harmonics present.
10. The sound intensity is the rate at which sound energy passes through unit area at right angles to the direction of the propagation of the wave.
11. The threshold of hearing is the smallest sound intensity detectable by the average human ear at a frequency of 1 kHz.
12. The Sound Intensity Level is a scale that compares a particular sound intensity to the threshold of hearing.
13. The dB(A) scale is a sound intensity level scale that has been adapted for the ear’s frequency response.
Light 1. Light is a form of energy that travels by electromagnetic waves.
2. Reflection of light is the way in which light ‘bounces’ off surfaces.
3. Diffuse reflection is the way in which light is reflected off an object that one would not normally regard as reflective.
4. Regular reflection is the way in which light reflects off smooth surfaces like mirrors.
