p6 - waves

• waves

  waves transfer energy from one place to another without transferring matter
• wavelength

  the distance of one entire oscillation

  when wave travels into more dense medium, wavelength decreases
• time period

  the time it takes for one entire oscillation
• frequency


  the number of complete oscillations per second

  measured in Hz

  frequency = 1/time

  when wave travels into more dense medium, frequency stays the same
• wave speed

  tells us how fast the wave is moving

  wave speed = frequency x wavelength
• transverse waves

  oscillations that are perpendicular to the direction of energy transfer

  examples:

  1. electromagnetic (radio, light)
  2. ripples
  3. waves of string
• longitudinal waves

  oscillations that are parallel to the direction of energy transfer

  examples:

  1. sound waves
  2. seismic P waves
• 3 things waves can do

  1. waves can be absorbed by material - energy from wave is transferred to material's energy stores
  2. waves can be transmitted - waves enter materials but carries on travelling (passes on to other side)
  3. waves can be reflected off surface - never enters the material
• angle of incidence = angle of reflection
• specular reflection


  • produces a clear image
  • normals are in the same direction
  • boundary is flat
• diffuse (scattered) reflection


  • boundary is bumpy
  • normals will be in different directions
  • light will be reflected in different directions
• refraction

  the change in direction of a wave as it passes from one medium (material) to another. caused by change in wave speed
• higher the density = slower the wave
• components in a refraction diagram

  1. point of incidence
  2. angle of incidence
  3. incidence ray
  4. refracted ray
  5. angle of refraction
  6. emergent ray
  7. normal
• light travels more slowly in more dense materials
• electromagnetic waves


  type of transverse waves

  in vacuum, will travel at same speed - 3x10^8 m/s

  in different medium, they'll travel at different speeds
• types of electromagnetic waves (7)


  1. radio waves
  2. micro waves
  3. infra red
  4. visible light
  5. ultra violet
  6. x-rays
  7. gamma rays
• trend in the electromagnetic table?

  left to right - frequency increases and wavelength decreases
• where does electromagnetic waves come from?

  gamma ray - radioactive decay

  visible light, ultra violet, x-rays - when electrons drop down energy levels

  infra red - bonds holding molecules together vibrate
• radio waves

  longest wavelength

  lowest frequency

  created using alternating current

  three types used for communications:

  1. long waves
  2. short waves
  3. very short waves
• what are oscilloscopes used for


  to display the wave frequency of an alternating current
• radio waves: long waves


  travels huge distances by diffracting (bending) around the curve surface of the earth
• radio waves: short waves


  travels long distances but can't curve around surface of earth

  travel by reflecting from ionosphere - electrically charged layer of the upper atmosphere
• radio waves: very short waves


  used in TV or FM Radios.

  travels directly from transmitter to receiver
• uses of electromagnetic waves

  • radio waves – television and radio

  • microwaves – satellite communications, cooking food

  • infrared – electrical heaters, cooking food, infrared cameras

  • visible light – fibre optic communications

  • ultraviolet – energy efficient lamps, sun tanning

  • X-rays and gamma rays – medical imaging and treatments.