Unit 3

• Waves


  Light, sound, heat - they all have wavelength, frequency, amplitude and speed in common
• Wavelength


  • The distance from one peak to the next
• Frequency


  • The number of complete waves passing a certain point per second, measured in hertz (Hz)
• Amplitude


  • The height of the wave (from rest to crest)
• Wave speed (velocity)


  • How fast the wave goes
• Period


  • The time it takes for one complete wave to pass a point
• Calculating wave speed


  Speed = Frequency x Wavelength
• You won't always be asked for the speed, so you might need the formula triangle too
• Finding the frequency of a light wave with wavelength 1x10^-7m

  • Speed of light = 3x10^8 m/s
• Waves often have high frequencies which are given in awkward units like kHz or MHz
• 900 MHz


  • 200,000,000 Hz
• Transverse waves


  • Vibrations are at 90 degrees to the direction the wave is transferred
• Longitudinal waves


  • Vibrations are in the same direction as the wave is transferred
• When a wave source is moving towards an observer

  The frequency of the wave they observe will be higher and the wavelength will be shorter than the original wave emitted by the source
• When a wave source is moving away from an observer

  The frequency of the wave they observe will be lower and the wavelength will be longer than the original wave emitted by the source
• This is called the Doppler effect
• Waves transfer energy and information without transferring matter
• It's important to understand diagrams of the two wave types and be able to distinguish between them