[Physics 2] Light

• relate to the behavior of wave to light

  What is light?
• Behavior of wave


  Relate the behavior of wave to light
• Properties of Light


  • Light travels in straight lines
  • Light travels VERY FAST – around 300,000 kilometres per second
  • Light travels much faster than sound
• At the speed of light, it can go around the world 8 times in one second
• Thunder and lightning start at the same time


  We will see the lightning first
• When a starting pistol is fired


  We see the smoke first and then hear the bang
• We see things because they reflect light into our eyes
• Shadows


  Places where light is "blocked"
• OPTICS


  The study of light and its properties
• OPTICS


  • Categorized as geometric optics or wave optics
  • In geometric optics, light is modeled as a ray
  • In wave optics, light is modeled as a wave
• Normal line


  A line perpendicular to the boundary of the two media at the point of incidence
• Angle of incidence


  The angle between the incident ray and the normal line
• Angle of reflection


  The angle between the reflected ray and the normal line
• Angle of refraction


  The angle between the refracted ray and the normal line
• Reflection


  Turning back of light to the original medium where it is propagating
• The angle of incidence is equal to the angle of reflection
• Specular reflection


  Reflection from smooth surfaces such as mirrors
• Diffuse reflection


  Reflection from rough surfaces
• Reflection


  • Sound waves bounce back as echoes from a wall or cliff
  • Moon's light is a reflection of the light of the sun
• Refraction


  The bending of a wave as it passes from one medium to another
• When a wave traveling a certain speed moves into another medium, it will either increase in speed or decrease in speed, resulting in a change in direction
• Laws of Refraction


  • Also known as Snell's Law
  • The incident ray, refracted ray and normal line lie in one plane
  • When a ray passes obliquely from an optically dense medium to a denser medium, it is refracted towards the normal
  • If light passes from an optically denser to a less dense medium, it will be refracted away from the normal
  • The relationship between the index of refraction and the angle with the normal is described in the Snell's Law
• Snell's Law


  1. Sample problem 1

  2. Sample problem 2

  3. Sample problem 3

  4. Sample problem 4