1. Course Info http://www.colorado.edu/physics/phys1230/phys1230_fa12/ Course Policies Calendar Office hours Instructor contact info Dr. Ellen Keister

2. Map to Help Room (G2B90) Lecture room Help room

3. Chapter 1 Light rays –Laser beam –Ray propagation Waves –Rope waves Wave medium Wave propagation –Other waves –Wave properties –Electromagnetic waves Light waves (EM waves) –Speed of light –Wavelength and frequency –Amplitude The Electromagnetic Spectrum –Visible light –Radio waves –Microwaves –Xrays

4. Light Rays Rays are a convenient descriptive tool Indicate the direction the light is traveling

5. Light Rays We only see light when a ray enters our eye

6. Light Rays: Bending Light rays bend when they pass from one material to another This is the principle behind lenses (chapter 3) Air Glass or water

7. Light Rays: Reflection Mirror Specular reflectionDiffuse reflection

8. Waves A wave is a propagating disturbance or oscillation The medium does not move very far, but the wave disturbance does

9. Rope Waves Disturbance has some speed, but rope segments do NOT move in direction of wave Rope segments move up and down, not in the same direction as the disturbance moves

10. Rays, Waves and Wavefronts The wavefront is defined as a curve or surface perpendicular (at a 90 o angle) to all the rays The wavefront is defined as a curve or surface perpendicular (at a 90 o angle) to all the rays OR, rays are drawn at right angles to the wavefront OR, rays are drawn at right angles to the wavefront

11. Wavefront Examples Let’s draw wavefronts for these rays: What type of light source might produce these rays? A laser Two light bulbs

12. Wave Properties Aperiodic wave Periodic wave

13. Periodic Wave Properties (Vocabulary) Wavelength (λ) Amplitude Ray: Direction of wave motion

14. Periodic Wave Properties (Vocabulary) Frequency (f) is the number of oscillations per second at a fixed point in space Frequency (f) is the number of oscillations per second at a fixed point in space Period (T) is the inverse of frequency, is the time it takes for one wavelength to pass a fixed point Period (T) is the inverse of frequency, is the time it takes for one wavelength to pass a fixed point Ray: Direction of wave motion

15. Clicker Question: Wavelength What is the wavelength of the red wave? A)1m B)2m C)3m meters

16. Clicker Question: Period meters What is the period of the red wave? A)2 milliseconds B)2 seconds C)2 minutes

17. Periodic Wave Properties: Speed For periodic waves, we can identify a speed (v) speed = distance/time speed = wavelength/period speed = Wavelength x frequency v = λf

18. Light Waves: Properties What do these properties mean for light waves? The amplitude of a light wave is related to its brightness Light waves are special. They have a constant speed over all colors, over billions of years, and over all brightness. We use the letter ‘ c ’ to denote the speed of light in a vacuum

19. Light Waves: Properties Recall: v = λf for light waves we use c = λf and ‘c’ never changes. Thus the wavelength and the frequency of light waves have a fixed relationship: λ = c/f or f = c/λ

20. Wavelength and Color The wavelength or frequency of light waves is related to the colors we perceive when the waves enter our eyes The wavelengths of light that our eyes and brain “see” are in the 400-700 nanometer (nm) range. One nanometer is 10 -9 meters

21. Clicker Question: Wavelengths The wavelength of green light is around 500 nm. How many wavelengths of green light fit into one centimeter (0.4 inches, about a fingertip)? a)20 thousand b)50 thousand c) Two million d)Two billion e)5 billion

22. Wavelength and Color Light with wavelength of 650 nm appears red when it enters a viewers eye Light with wavelength of 520 nm appears green when it enters a viewers eye Light with wavelength of 470 nm appears blue when it enters a viewers eye

23. Clicker questions Which of the light waves has the longest wavelength? Which of the light waves is brightest? Which of the light waves has the highest speed in empty space? a) b) c) d) They all have the same speed a) b) c)

24. Clicker question What does the viewer see when the wave at left with wavelength 650 nm goes by him? a)Red b)Blue c)Green d)White e)Nothing

25. What happens when two or more waves with different wavelengths reach your eye? Light with both wavelengths 650 nm and 520 nm appears yellow when it enters a viewers eye Light with only wavelength 580 nm also appears yellow when it enters a viewers eye

26. What is white light? Light which is a mixture of 650, 520 and 470 nm wavelengths (and possibly more wavelengths) appears white when it reaches your eye No single wavelength (mono-chromatic) wave appears white when it reaches your eye!

27. White Light through a Prism A prism spreads out the over- lapping wavelengths in white light into different spatial locations where they can be seen as colors. 400 nm 700 nm