Waves, Light and Sound
What this domain tests
Waves, Light and Sound tests wave properties, reflection, refraction, diffraction, interference, sound, lenses and optical applications.
Core rules
- v = fλ; period T = 1/f; amplitude is maximum displacement; wavelength is the distance between successive crests.
- Transverse waves oscillate perpendicular to the direction of travel; longitudinal waves such as sound oscillate parallel.
- Reflection: angle of incidence equals angle of reflection, both measured from the normal.
- Refraction: n = sin i ÷ sin r. Light bends towards the normal when entering a denser medium. Frequency stays constant; speed and wavelength change.
- Total internal reflection occurs above the critical angle when light travels from a dense to a less dense medium; it is used in optical fibres.
- Sound needs a medium. Higher frequency gives higher pitch; larger amplitude gives louder sound.
Worked example
A sound wave has frequency 500 Hz and wavelength 0.68 m. v = fλ = 500 × 0.68 = 340 m/s. If it enters water where the speed is 1500 m/s, the frequency remains 500 Hz, so the new wavelength is 1500 ÷ 500 = 3.0 m. The wave bends away from the normal because it speeds up.
Traps
Always measure angles from the normal, not the surface. Do not change frequency during refraction. Do not say sound travels through a vacuum. In ray diagrams, draw at least two rays and label the image clearly.