1. Light Waves and Color Metro Community College 9/19/2015

2. Electromagnetic Waves Maxwell predicted that an electric dipole would transmit changing electric and magnetic fields if a changing current was sent back and forth along the dipole. His equations proposed that light traveled at the same speed in all reference frames. 7/23/2010Lyle A Sass2

3. What is an electromagnetic wave? Electromagnetic waves are transverse electric field waves in phase with magnetic field waves that travel away from the source at the speed of light in the medium. 7/23/2010Lyle A Sass3

4. What is the speed of an electromagnetic wave? The speed of light, c is 3 X 10-8 m/s. the speed of light in medium is c/n where n is the index of refraction of the material. 7/23/2010Lyle A Sass4

5. What is the frequency of an electromagnetic wave? The speed of light for our calculations is 3 X 10 8 m/s. The formula is v = f The formula for the energy of an electro- magnetic quantum is E = hf where h = 6.626X10 -34 J-s 7/23/2010Lyle A Sass5

6. Wavelength and Color 7/23/2010Lyle A Sass6

7. Transmission and Reception Transmission Long wave – dipole AM Radio – AM transmitter varying the amplitude by changing energy FM Radio – FM transmitter varying the frequency of each wave. TV – Medium is changing Infrared-light-ultraviolet – atom emission. Reception Radio wave – dipole AM receiver – to speaker, current varies with amplitude of wave. FM receiver – various frequency waves become speaker frequencies TV Medium is changing Diodes in eye, cameras. Chemical changes in film. 7/23/2010Lyle A Sass7

8. Transmission and Reception Transmission Ultraviolet – Atomic and accelerated electron emissions X-rays – emissions by accelerating electrons Gamma rays – emissions by nuclei Reception Molecules with proper energy levels, skin cells, and etc. Radiographic Film, photo sensors Electron collisions in material 7/23/2010Lyle A Sass8

9. Eye Perception of Light 7/23/2010Lyle A Sass9

10. Reflection of Light Types of Reflection Diffuse Specular Diffraction Thin Film Images differ from each one type of reflection. 7/23/2010Lyle A Sass10

11. Transmission of Light Types of transmission Diffuse – Scattering – Frosted glass Direct – clear glass Diffraction single slit Interference– – double slit – grating Thin film Examples 7/23/2010Lyle A Sass11

12. Transmission of Light Types of transmission Diffuse – Scattering – Frosted glass Direct – clear glass Diffraction single slit Interference– – double slit – grating Thin film Examples 7/23/2010Lyle A Sass12

13. Interference of Light Waves The bright lines occur where the light is in phase and the path difference is one wavelength. The dark lines occur where the light is in phase and the path difference is one-half wavelength. Path difference = d(y/x) = d(y/x) => bright /2 = d(y/x) => dark 7/23/2010Lyle A Sass13

14. Diffraction and Gratings 7/23/2010Lyle A Sass14 y/x = (w/2)/ /2

15. Polarized Light Polarized Light – has the electric field set in a particular orientation. A second polarized can block the electric field completely. 7/23/2010Lyle A Sass15

16. Color Mixing Subtraction – Pigment mixing subtracts. Total subtraction gives black. Addition – light mixing results in the addition of light. Total addition results in white 7/23/2010Lyle A Sass16

17. Scattering Noon sun has less dust to come through, so it is yellow. Sunset sun is red because it passes through the most dust and all long wavelengths are scattered 7/23/2010Lyle A Sass17 The short wavelength light (near the blue end of the spectrum) is scattered from the dust in the air.

18. Birefringence Certain materials polarize light passing through them in proportion to the stress on the material. Stress test – by putting the materials between crossed polarizing lenses. Light that is polarized again by the material will pass through. Since the amount of polarization depends on the wavelength the light that passes through appears in different colors. 7/23/2010Lyle A Sass18

19. Summary Electromagnetic waves Wavelength and color Interference of light waves Diffraction and gratings Polarized light 7/23/2010Lyle A Sass19