Waves and EM Spectrum

• Waves

  Transfer energy without transferring matter
• Waves


  • Water waves at the beach
  • Electromagnetic waves
• Wave

  • Crests (tall bits)
  • Troughs (low bits)
  • Amplitude (height from rest position)
  • Wavelength (distance between crests)
• Frequency


  Number of wavelengths that pass a point per second
• Calculating frequency


  Divide velocity by wavelength
• Units


  • Frequency - Hertz
  • Wavelength - Meters
  • Velocity - Meters per second
• Types of waves


  • Transverse waves
  • Longitudinal waves
• Transverse waves

  • Vibrations go up and down
• Longitudinal waves


  • Vibrations go left and right
  • Have compressions (vibrations close together)
  • Have rarefactions (vibrations far apart)
• Transverse waves


  • Light waves
  • Water waves
  • Waves on the electromagnetic spectrum
• Longitudinal waves


  • Sound waves
  • P-waves (seismic waves)
• Sound wave pitch

  • High pitch = short wavelengths
  • Low pitch = long wavelengths
• What can happen when a wave hits a new material

  • Transmitted (passes through)
  • Absorbed (object absorbs wave)
  • Reflected (wave bounces back)
• Refraction


  1. Wave changes speed and direction when entering new material

  2. Frequency does not change
• Refraction


  • Angle of incidence
  • Angle of refraction
• Reflection


  1. Wave bounces back off material

  2. Angle of incidence = Angle of reflection
• Types of reflection


  • Specular (flat surface, uniform reflection)
  • Diffuse (uneven/rough surface, scattered reflection)
• Uses of reflection


  • Ultrasound (high-pitched sound waves reflected back)
• Electromagnetic spectrum


  Range of all transverse waves depending on frequency
• Visible light


  • Small part of electromagnetic spectrum
  • Only part human senses can detect
  • Red light = low frequency, blue light = high frequency
• White light is made up of all colors on the spectrum
• Object color

  Reflects the color we see, absorbs other colors
• Black objects


  Absorb all light
• Transparent/translucent objects


  Allow most light to pass through
• Lenses


  • Convergent (bring light to a focus point)
  • Divergent (spread light out)
• The lens in the eye is a convergent lens