Waves

• What are TRANSVERSE waves?


  • oscillations are perpendicular to the direction of energy transfer
  • e.g light waves
  • waves have peaks and troughs
• What are LONGITUDINAL waves?


  • oscillations are parallel to the direction of energy transfer
  • e.g. sound waves
  • waves have compressions and rarefactions
• What is the AMPLITUDE of a wave?


  Maximum displacement from the equilibrium position
• What is the WAVELENGTH of a wave?


  The distance between the same points on adjacent waves
• What is the FREQUENCY of a wave?


  The number of complete waves passing a point per second
• Equation that links TIME PERIOD and FREQUENCY

  Frequency =$\frac{1}{Time\ period\ }$
• Equation that links WAVE SPEED, FREQUENCY and WAVELENGTH

  Speed = frequency x wavelength
• What is the ANGLE OF INCIDENCE?


  All angles are measured to the normal angle of reflection
• What is REFRACTION?


  When light travels at different speeds leading it to bend
• What are ELECTROMAGNETIC waves?


  • oscillating electric and magnetic field
  • transverse waves
  • can travel in a vacuum
  • very wide range of frequencies and wavelengths
• What is the order of the different types of electromagnetic waves?

  1. Radio
  2. Microwave
  3. Infrared
  4. Visible Light
  5. Ultraviolet
  6. X-ray
  7. Gamma rays
• What are RADIO waves?


  Results from oscillating electric currents

  • alternating current in wires (transmitters)
  • radio waves can induce alternating current in wire (receiver)
  • The AC has the same frequency as the radio waves (50Hz)

  Used for communication

  • radio
  • Bluetooth
  • television
• In terms of Infrared radiation - Room Temperature 


  Absorbing and emitting IR ate the SAME rate
• In terms of Infrared Radiation - Hot conditions

  Emitting IR at a HIGHER rate than absorbing IR
• In terms of Infrared Radiation - Cold conditions

  Absorbing IR at a HIGHER rate than emitting IR
• How do we hear?

  1. sound waves vibrate our eardrum at the same frequency
  2. vibrations are passed through structures in our ear
  3. These vibrations are converted into electrical signals
  4. Electrical signals are sent to the brain
• What is a perfect 'black body'?

  A perfect black body absorbs all the EM radiation that hits it
• What are 'Ultrasound' waves?

  Sound waves with frequencies greater than 20 kHz

  • allow us to see through things that do not transmit light
• What are 'P-Waves'?

  • primary waves
  • travel the fastest
  • longitudinal
  • travel in solids and liquids
  • faster in solids than liquids
  • refract
• What are 'S-Waves'?

  • Secondary waves
  • travel slower than P waves
  • Transverse
  • only travel in solids
  • travel faster in dense objects
  • refract
• How does the color of a surface affect the IR emission rate?

  Black and matte surfaces= best absorbers and emitters of IR radiation

  White and Shiny surfaces= worst absorbers and emitters of IR radiation
• Why does a Red object look red?

  It will absorb all colors except red will be reflected
• What color will a green object look like in a red filter?

  Black because it will absorb all the colours
• What is the range of human hearing?

  20 Hz - 20 kHz
• What are Microwave waves?

  Oscillating electric currents

  • used to heat food
  • used for communication
• What are Infrared waves?

  Results from the movement of atoms

  • all objects continuously emit and absorb IR
  • used to detect heat
  • hotter = emit more IR
• What are Visible Light waves?

  Results from changes in atoms

  • continuous spectrum
  • red= longest wavelength, low frequency
  • violet= shortest wavelength, high frequency
  • white light has all colours
  • used in fiber optic communication
• What are Ultraviolet waves?

  Results from changes in atoms

  • can cause fluorescence
  • used for security
  • Can be harmful - premature skin ageing, skin cancer
• What is X-Ray?


  Result from changes in atoms

  • Used to take medical images
  • Used to treat cancer (radiotherapy)
  • Can be harmful- high frequency, high energy, ionizing, damage cells
• What are Gamma Rays?

  Result from changes in the nucleus

  • Used as a medical tracer
  • Used to treat cancer (radiotherapy)
  • Can be harmful- high frequency, high energy, ionizing, damage cells
• Which wave has the shortest wavelength on the electromagnetic spectrum?

  Gamma Rays
• Which wave has the longest wavelength on the electromagnetic spectrum?

  Radio waves
• Words to describe an image on a ray diagram (concave lens)

  1. virtual
  2. diminished
• What are concave (diverge) lenses used for?

  Short-sightedness - causes rays of lights to spread out
• What are convex (converging) lenses used for?

  Long-sightedness - causes rays of light to be brought together at the principal focus
• In reflection, the angle of incidence is always ________ the angle of reflection.

  Equal to
• What is Refraction?

  The change in direction of a wave caused by the change of speed
• What is the law of reflection?

  angle of incidence = angle of reflection
• What is specular reflection?

  Reflection from a smooth, flat surface
• What is diffuse reflection?

  Reflection from a rough, unflat surface. Light is scattered in all directions.