Waves and EM spectrum phy

• Waves


  • Water waves at the beach
  • Electromagnetic waves
• Transverse waves


  • Vibrations go up and down
• Longitudinal waves


  • Vibrations go left and right
• Longitudinal waves


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


  Has short wavelengths
• Low pitch sound wave


  Has long wavelengths
• What can happen when a wave encounters a new material

  1. Transmitted

  2. Absorbed

  3. Reflected
• Refraction


  Change in direction of a wave when it passes from one medium to another
• Refraction


  • Frequency does not change
• Angle of incidence


  Angle at which a wave enters a new material
• Angle of refraction

  Angle at which a wave changes direction when entering a new material
• Reflection


  • Angle of incidence = Angle of reflection
• Specular reflection


  Uniform reflection off a flat surface
• Uses of reflected waves


  • Ultrasound (high frequency sound waves)
• Electromagnetic spectrum


  Range of all transverse waves depending on their frequency
• Visible light


  • Small part of the electromagnetic spectrum that human senses can detect
• Red light has low frequency, blue light has high frequency
• All colors of visible light combined form white light
• Object color


  The color that is reflected, all other colors are absorbed
• Black objects


  Absorb all light
• Transparent/translucent objects


  Allow most light to pass through
• Convergent lenses


  • Bring light waves together to a focus point
• Divergent lenses


  • Spread light waves out in different directions
• Electromagnetic (EM) waves


  • Transverse
  • Also called EM radiation
  • Consist of vibrating electric and magnetic fields
  • Travel through a vacuum at 3 x 10^8 m/s

  
• The higher frequency waves are more dangerous
• Ionising radiation can kill cells completely, leading to radiation sickness
• Transparent objects


  Transmit light in straight lines so images are clear

  
• Translucent objects


  Transmit light but also scatter some so images aren't seen clearly

  
• Filters


  Only transmit certain wavelengths and absorb other wavelengths
• Blue filter


  • Only allows blue light to pass through
• Radiation emitted by objects

  • Has a range of wavelengths
  • As the temperature of an object increases, the intensity of every emitted wavelength increases

  
• During the day


  More radiation is absorbed than emitted from Earth

  
• During the night


  Less radiation is absorbed than emitted from Earth
• By this mechanism, the overall temperature of the Earth's surface should be constant
• Black surfaces


  Absorb more infrared radiation and so heat up quicker
• White and shiny surfaces

  Reflect infrared radiation so do not heat up as quickly
• Specular reflection


  Parallel waves are reflected in a single direction by a smooth surface

  
• Mirror


  • Gives a clear image in the reflection

  
• Diffuse reflection


  Parallel waves are reflected by a rough surface and the reflected rays are scattered in lots of different directions
• For each ray, the angle of incidence is equal to the angle of reflection