P5 Waves

Wave Behaviour

• Wave is an oscillation that transfers energy.
• Mechanical waves need a medium to travel through.
• Longitudinal (Sound Waves) - The direction of vibration of individual air molecules is the same as the direction of the wave.
• Transverse (Light Waves) - The direction of the vibration is at right angles to the direction of travel of the wave.
• Amplitude - displacement from the rest position of a wave to the trough or the crest.
• Wavelength - distance from one point in a wave to the same point on the next wave. (Crest - Crest) (Trough - trough)
• Frequency - Number of oscillations per second
• Time period - time for 1 wave to pass a given point. Calculated by = 1/frequency.

Wave Velocity

• IMAGINE RUNNING ALONG A TRACK, STRIDE IS 1.5 METRES LONG AND YOU TAKE 2 STRIDES EACH SECOND.
• In terms of waves, your 'stride' represents the wavelength, and 'strides per second' represent that frequency.
• wave velocity (m/s) = frequency (Hz) X Wavelength (m)
• Measuring the wavespeed of sound?
• Calculate the wavelength by freezing the waves. Stop the motor vibrating to produce any more waves.
• On the paper, there is displayed image of wavelength. Measure the first wave to the last wave and divide by how many waves there are.
• In addition, to calculate frequency, start timer e.g for 10 secs. Then stop, calculate frequency by dividing by 10. to calculate frequency per second.
• Wavelength x frequency = wavespeed of water waves in ripple tank.

Sound Properties and Uses

• Refraction - when the speed and direction of a wave changes as it passes through a more or less dense medium.
• If the wavespeed/velocity increases, and the wavelength also increases, the frequency stays the same.
• A soundwave that hits the boundary at O degrees to the normal will speed up but will not change direction.