Light and Reflection

1
Light and Reflection

• Chapter 14, Sections 1 2
• Pg. 520-539

2
Characterization of Light

• Light has both a wavelike and particle like
  nature.
• Electromagnetic wave theory Light is a wave
  composed of oscillating electric and magnetic
  fields (electromagnetic wave).
• These waves propagate transversely at right
  angles to each other.

3
Characterization of Light
4
Characterization of Light

• All electromagnetic waves travel at the speed of
  light (c).
• c 3.0 x 108 m/s
• Electromagnetic waves vary depending on frequency
  and wavelength.
• These differences account for the broad range in
  the electromagnetic spectrum.

5
Electromagnetic Spectrum
6
Characterization of Light

• The same relationship between frequency,
  wavelength, and speed that exists in sound waves
  or objects undergoing SHM also holds true for
  electromagnetic waves.

? f ? (Chapter 12)
c f ?
7
Characterization of Light

• Huygens Principle
• Electromagnetic waves travel in wave fronts.
• Wave fronts are made up of many wavelets, each
  containing a point source. If you make a line
  tangent to each point source, you have identified
  a new wave front.

8
Characterization of Light

• Huygens Principle describe waves interacting
  with matter (diffraction) or waves moving in a
  straight line.
• The perpendicular direction in which the wave
  front is moving is referred to as a ray.

9
Characterization of Light
Wave front motion as it moves around an object
10
Characterization of Light

• Light becomes more spread out and there is less
  light available per unit area.
• Inverse relationship between brightness and
  distance.
• Brightness decreases by the square of the
  distance from the source.
• ex. There is ¼ as much light falling on a
  particular spot 2 m away than there is light
  falling on the same spot that is 1 m away. (fig
  14-4 pg. 525)

11
Reflection

• The turning back of an electromagnetic wave
  (light ray) at the surface of a substance.
• Depending on how smooth the reflecting surface
  is, the reflection will either be diffuse or
  specular.

12
Reflection

• Reflections off flat surfaces follow 2 simple
  rules
• angle in (incidence) equals angle out
  (reflection)
• angles measured from the surface (normal)

13
Reflection

• Using the basic rules of reflection, we can
  create virtual images.
• Virtual images are images formed by light rays
  that appear to intersect.
• ex. Looking in a mirror
• Image location can be predicted with ray
  diagrams.

14
Reflection
Ray diagram of mirror image (full length mirror)