Waves

• Waves transfer energy and information without transferring matter


  Complete this sentence: Waves transfer ______ and ______ without transferring _______.
• Frequency


  The number of waves passing through a point per second. Units: Hz (hertz)
• Wavelength


  The distance between two adjacent peaks on a wave.
• Amplitude


  The maximum displacement of the wave from its equilibrium position. The distance between the centre of the wave and a peak.
• Period of a wave

  The length of time it takes for one full wave to pass through a point.
• Wave speed calculation


  Wave speed (measured in metres per second) is equal to the product of the wavelength and the frequency of the wave. Formula: Wave velocity = f × λ
• Longitudinal wave


  Vibrations parallel to the direction of energy transfer. Examples: sound waves, earthquakes (seismic waves).
• Transverse wave


  A wave with oscillations perpendicular to the direction of energy transfer. Examples: electromagnetic waves.
• Doppler effect


  When a wave source moves towards the observer, observed frequency increases and wavelength decreases; when moving away, observed frequency decreases and wavelength increases.
• Speed of electromagnetic wave in vacuum

  3 x 10^8 m/s.
• Electromagnetic waves transfer


  Energy and information.
• Properties of electromagnetic waves

  All are transverse, transfer energy/information, travel at speed of light in vacuum, can be reflected, refracted, or diffracted.
• Longest wavelength in electromagnetic spectrum

  Radio waves.
• Visible light spectrum colors

  Red, Orange, Yellow, Green, Blue, Violet.
• Uses of radio waves

  Communication through radio, satellite transmissions.
• Uses of microwaves


  Cooking in microwaves ovens, communications, satellites.
• Infrared spectrum uses


  Cooking, thermal imaging, television remote controls.
• Uses for visible light


  Vision, photography, optical fibers (endoscope, communication).
• Ultraviolet spectrum uses


  Security marking, fluorescent lamps.
• X-ray uses


  Scanners at airports, medical x-ray machines.
• Gamma rays uses and disadvantages

  Sterilize food/medical equipment, cancer diagnosis; can cause mutations or cell damage.
• Disadvantages of microwaves


  Can cause heating of internal body tissues.
• Danger associated with electromagnetic waves

  Increases with frequency.
• Dangers of excessive UV exposure

  Damage to eyes/skin cells, leading to cancer or eye conditions.
• Normal (reflection and refraction)


  A vertical imaginary line perpendicular to the boundary.
• Reflection off a boundary

  Light bounces off a smooth flat surface, angle of incidence equals angle of reflection.
• Refraction through different media

  Light changes speed/direction in new medium; if denser, bends towards normal; if less dense, bends away from normal.
• Equation for angle of incidence, angle of refraction, refractive index

  n: refractive index, i: angle of incidence, r: angle of refraction.
• Critical angle


  Angle causing reflection angle to be 90 degrees, light refracts onto boundary.
• Equation for critical angle and refractive index

  n: refractive index, c: critical angle.
• Total internal reflection


  Reflection back to less dense medium when angle of incidence is larger than critical angle between media.
• Uses of total internal reflection


  Endoscopes, periscopes, optical fibers, cat eye reflectors, shining of diamonds.
• Light refracting at 90 degrees

  No refraction occurs.
• Amplitude

  The maximum displacement of the wave from the rest position

  
• Wavelength


  The distance from one point in the wave to the identical point on the next wave e.g crest to crest or compression to compression

  
• Frequency


  The number of complete wave cycles passing a point in one second
• Period


  The time it takes to complete one cycle.

  The time it takes for a wave to travel one wavelength.
• Equation for Wave Speed (m/s)


  Frequency (Hz) x wavelength (m)
• Equation for Frequency (Hz) and Time period (s)


  frequency (Hz) = 1/Time period (s)
• Hertz (Hz)


  Unit of frequency