Electromagnetic Waves

• Electromagnetic Waves


  . Electromagnetic (EM) waves are transverse waves

  . All types of electromagnetic wave travel at the same velocity (the speed of light) in air or a vacuum

  . The electromagnetic spectrum extends from low frequency, low energy waves to high frequency, high energy waves

  . Human eyes are only capable of detecting visible light, i.e. a very limited range of electromagnetic waves

  . The wavelength of an electromagnetic wave affects how it is absorbed, transmitted, reflected or refracted by different substances. This affects its uses
• Key Point


  All electromagnetic waves have the same velocity speed in air or a vacuum
• Refraction


  When a wave passes from one medium into another it can be refracted and change direction
• Refraction


  • The direction of refraction depends on the angle at which the wave hits the boundary
  • The direction of refraction depends on the materials involved
• Refractive index


  The way in which a material affects refraction of light rays
• Light travels from a material with a low refractive index to one with a higher refractive index


  It bends towards the normal
• Light travels from a material with a high refractive index to one with a lower refractive index


  It bends away from the normal
• Refraction


  It is due to the difference in the wave speed in the different media
• When a light wave enters, at an angle, a medium in which it travels slower


  1. The first part of the light wave to enter the medium slows down

  2. The rest of the wave continues at the higher speed

  3. This causes the wave to change direction, towards the normal
• You need to be able to show refraction using a wave front diagram
• Key Point


  When slowing down, the wave is refracted towards the normal. When speeding up, it is refracted away
• Key Point


  A common error is to draw the ray refracting onto or even past the normal. This never happens and will lose marks in the exam
• Refraction


  What happens when a wave reaches a boundary between one medium (material) and another
• Ray diagrams


  Used to show what happens when a wave reaches a boundary between one medium and another
• Constructing a ray diagram

  1. Rays must be drawn with a ruler

  2. Each straight section of ray should have a single arrow drawn on it to indicate the direction of movement

  3. Where the ray meets the boundary, a 'normal' should be drawn at right-angles to the boundary

  4. All relevant angles should be labelled
• Ray diagrams


  • Used whenever a diagram is needed to represent how light moves from one place to another, e.g. reflection