The basics of waves, EM waves (pg 27-31)

• Wavelength (λ) is the distance from one peak to the next.
• Frequency (f) is how many complete waves there are per second (passing a certain point). It's measured in hertz (Hz): 1Hz is 1 wave per second.
• Amplitude (A) is the height of the wave (from rest to crest).
• The speed (v) is how fast the wave goes.
• The period (T) is the time it takes in seconds for one complete wave to pass a point.
• $v =$$f *$$λ$
• Speed (m/s) = Frequency (Hz) * Wavelength (m)
• Waves can be transverse or longitudinal.
• Most waves are transverse. Examples:

  1. Light and all other EM waves.
  2. A slinky spring wiggled up and down.
  3. Waves on strings.
  4. Ripples on water.
• In transverse waves the oscillations are at 90º to the direction energy is transferred by the wave.
• Examples of longitudinal waves:

  1. Sound and ultrasound.
  2. Shock waves.
  3. A slinky spring when you push the end.
• All waves transfer energy and information in the direction they're travelling without transferring matter.
• Waves can be used as signals to transfer information from one place to another.
• There are seven types of electromagnetic waves:

  A) radio waves

  B) microwaves

  C) infrared

  D) visible light

  E) ultraviolet

  F) x-rays

  G) gamma rays

  H) increasing frequency and decreasing wavelength

  
• Electromagnetic waves with different wavelengths have different properties. They're grouped depending on their wavelength.
• All types of EM radiation are transverse waves and travel at the same speed through free space (a vacuum).
• The different colors of visible light depend on the wavelength - red has the longest wavelength (and lowest frequency) and violet has the shortest wavelength (and highest frequency).
• Colors in order of increasing frequency and decreasing wavelength:

  red, orange, yellow, green, blue, indigo, violet.
• Displacement (s) is the distance from the equilibrium position.
• Radiowaves: used for communication and controlling model aeroplanes.
• Microwaves: used for cooking food and for satellite transmissions. Mobile phones use microwaves.
• Infra red (a.k.a heat radiation): Used in night vision equipment, remote controls and to heat things up.
• Visible light: used to see with and transmit information down optical fibres.
• Ultra violet: used for security marking property, disco effects and fluorescent lamps.
• X-rays: used to look inside the body. X-rays can pass easily through flesh, but not through bone. Also used in airport security.
• Gamma rays: Used to kill harmful bacteria so that food keep fresher for longer, sterilising hospital equipment and treating cancer.
• The higher the frequency of EM radiation, the more energy it has, and generally the more harmful it can be.
• Microwaves heat human body tissue internally.
• Infra red radiation can cause skin burns.
• Ultraviolet radiation can damage surface cells and cause blindness.
• Gamma rays can cause cell mutation or destruction, leading to tissue damage or cancer.
• Electromagnetic waves travel at the same speed in free space.
• The Doppler effect is the change in the observed frequency/ wavelength of a wave due to the wave source moving towards or away from the observer.
• Sound and light waves can be reflected and refracted.
• The Doppler effect occurs when there is relative motion between the source waves and the observer of the waves.