Waves and Sound: notes

Waves

• Wave speed: v = fλ. A 50 Hz wave with wavelength 6 m moves at 300 m/s.
• Frequency: waves per second, in hertz (Hz). Amplitude: the maximum displacement from the rest position.
• Transverse wave: vibration at right angles to the direction of travel, such as water waves and light.
• Longitudinal wave: vibration along the direction of travel, such as sound.

Wave behaviour

• Reflection: the angle of incidence equals the angle of reflection.
• Refraction: a wave changes speed and bends when it enters a new medium.
• Diffraction: a wave spreads out when it passes a gap or edge. It spreads most when the gap is about one wavelength wide.

Sound

• Needs a medium: sound cannot travel through a vacuum.
• Speed: about 330 m/s in air, faster in liquids and fastest in solids.
• Pitch: set by frequency. Loudness: set by amplitude.
• Echo: reflected sound. Humans hear 20 Hz to 20 000 Hz; above that is ultrasound.