1. Wave Properties of Light

2. Characterization of Light Light has both a wavelike and particle like nature. 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). 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. These waves propagate transversely at right angles to each other.

3. Oscillating Magnetic Field Oscillating Electric Field Characterization of Light

4. All electromagnetic waves travel at the speed of light (c). All electromagnetic waves travel at the speed of light (c). c = 3.0 x 10 8 m/s Electromagnetic waves vary depending on frequency and wavelength. Electromagnetic waves vary depending on frequency and wavelength. These differences account for the broad range in the electromagnetic spectrum. These differences account for the broad range in the electromagnetic spectrum. Characterization of Light

5. Electromagnetic Spectrum

6. The same relationship between frequency, wavelength, and speed that exists in sound waves or objects undergoing SHM also holds true for electromagnetic waves. The same relationship between frequency, wavelength, and speed that exists in sound waves or objects undergoing SHM also holds true for electromagnetic waves. Characterization of Light ν = f λ (classic wave speed equation) c = f λ

7. Huygen’s Principle Electromagnetic waves travel in wave fronts. Electromagnetic waves travel in wave fronts. Wave fronts are made up of many wavelets, each containing a “point source”. Wave fronts are made up of many wavelets, each containing a “point source”. Characterization of Light

8.  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. Wave front motion as it moves around an object Characterization of Light

10. What is the relationship between brightness and the distance from a light source?

11. Brightness decreases by the square of the distance from the source. Brightness decreases by the square of the distance from the source. Inverse square relationship 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. Characterization of Light

12. Refraction of Light

13. What is Refraction? Refraction is the bending of light as it travels from one medium to another. Refraction is the bending of light as it travels from one medium to another.

14. Refraction In vacuum, light travels with a speed In vacuum, light travels with a speed c = 3.00 x 10 8 m/s In a transparent medium, (ex. water or glass) the speed of light is slower than its speed in vacuum. In a transparent medium, (ex. water or glass) the speed of light is slower than its speed in vacuum. WHY? Ans. interactions between photons WHY? Ans. interactions between photons and molecules of the medium and molecules of the medium

15. What does this have to do with refraction? The difference in speed causes light rays to bend (refracted ) when traveling across different transparent materials!!! The difference in speed causes light rays to bend (refracted ) when traveling across different transparent materials!!!

16. Refraction Air Glass Higher speed (lower index of refraction) Lower speed (higher index of refraction) Refracted ray bends towards the normal θiθiθiθi Normal θrθrθrθr

17. Air Glass Normal Higher speed (lower index of refraction) Lower speed (higher index of refraction) Refraction θiθiθiθi θrθrθrθr Refracted ray bends away from the normal

18. What is “index of refraction”? The index of refraction ( n) is the ratio of the speed of light ( c) in vacuum to that of the speed ( v) in the medium. The index of refraction ( n) is the ratio of the speed of light ( c) in vacuum to that of the speed ( v) in the medium. n = c/v

19. Sample Problem What is the speed of light in a diamond if its index of refraction is 2.419? n = c/v n = 2.419 c = 3.00 x 10 8 m/s v = c/n = 3.00 x 10 8 m/s / 2.419 ≈ 1.24 x 10 8 m/s

20. Ok…… so how is knowing about refraction useful?Image NEMO Mmmm..……. Fish and Chips!!! Normal

21. How can we figure out the angle of our refracted ray? We use Snell’s Law We use Snell’s Law n i (sin θ i ) = n r (sin θ r ) Willebrord van Roijen Snell (1580-1626)

22. Sample Problem A light ray traveling through the air strikes a smooth slab of glass at an angle of 30° to the normal. Find the angle of refraction. Air Glass θiθi Normal θrθr θ i = 30° n i (air) = 1.00 n r (glass) = 1.52 n i (sin θ i ) = n r (sin θ r ) 1.00(sin 30) = 1.52 (sin θ r ) θ r = sinˉ¹ [(1.00 (sin 30)) / 1.52] = 19.2°