1. Unit on Light Chapter 14 – Light and Reflection Chapter 15 – Refraction Chapter 16 –Interference and Diffraction

2. Chapter 14 The Nature of Light “Light” comes in a wide variety of frequencies and wavelengths. What is constant? Speed – all form of EM Radiation travel at the same speed – 3.0 x 10 8 m/s Visible Light – very narrow range of light that humans can 4.3 x 10 14 Hz -- 7.5 x 10 14 Hz EM video

3. Electromagnetic Waves (EM) – Transverse Waves - Oscillating electric and magnetic fields moving at right angles to each other – perpendicular to motion of wave

4. Electromagnetic Spectrum (EM) Long wave lengths (low frequencies) Short wave lengths (high frequencies)

6. Dual Nature of Light (Electromagnetic Energy) behaves as both a wave and a particle  EM radiation travel as waves and move energy EM radiation is also a stream of particles called photons – bundles of energy.  MAX PLANCK – (1900) Black Body Radiation - If you heat an object it will begin to give off light.  Planck concluded that light is ‘quantized’.  This means that it gives off energy that is proportional to its frequency.

7. As temp increases total energy given off an object increases and the peak shifts to shorter wavelengths E Photon = h f h = Planck’s constant = 6.63 x 10 -34 J x s

8. Energy of a Photon

9. Einstein used Planck’s idea to explain the PHOTO ELECTRIC EFFECT When light hits a metal, electrons ( e- ) are given off.

10. The Kinetic Energy of the electron depends on the COLOR of the light, NOT its BRIGHTNESS. EINSTEIN There is a Threshold Energy which is the minimum energy needed to knock the electrons off. Any extra energy became the K.E. of the e-

11. Example From the equation ( E = h  f ) and the equation for waves we have: λ x f = c ( speed of light = 3 x 10 8 m/s ) E = h  f COLOR λ(m) f (Hz) E(J) I.R 8.0 x 10 -7 _______________ Red ________ 4.6 x 10 14 _______ Yellow 5.7 x 10 -7 _______________ Green________5.9 x 10 14 _______ Blue 4.7 x 10 -7 _______________ Violet________7.0 x 10 14 _______

12. Example From the equation ( E = h f ) and the equation for waves we have: λ x f = c ( speed of light = 3 x 10 8 m/s ) (in a vacuum) but as light passes through a medium it slows down COLOR λ(m) f (Hz) E(J) = h x f I.R 8.0 x 10 -7 3.75 x 10 14 2.49 x 10 -19 Red 6.52 x 10 -7 4.6 x 10 14 ________ Yellow 5.7 x 10 -7 5.26 x 10 14 ________ Green5.1 x 10 -7 5.9 x 10 14 ________ Blue 4.7 x 10 -7 6.38 x 10 14 ________ Violet4.29 x 10 -7 7.0 x 10 14 _________

13. MATTER and ENERGY Einstein used his famous equation E = m x c 2 (energy and mass are equivalent!) and Planck’s equation ( E = h x f )to determine that PHOTONS do have MASS! m x c 2 = h x f (substitute for f = c/λ ) m photon = h c x λ

14. LOUIS de BROGLIE – p. 466  Took Einstein’s and Plank’s ideas and said that maybe ALL matter has wavelike properties not just particle like properties.  If matter has a velocity, then it has a wavelength. de Broglie’s wavelength: Formula: λ = h = h p m x v p = momentum h = Planck’s constant m = mass of photon v = velocity

15. Photoelectric Effect light as particle and wave

16. Lower frequencies travel ___________ Faster (red light) Higher frequencies travel ___________ Slower (blue light) WHY?  Lower frequencies don’t make the e- “jump” as far.  Higher frequencies make the e- “jump” to higher levels – but they take more time to do this, or they may cause ionization (e- jumps off the atom altogether ). Electron Dance – light propagating through a medium

17. Seeing Colors  When you see a wavelength of 550 nm your brain interprets green.  Objects reflect certain wavelengths and absorb others.  “White” light passed through a prism – or a diffraction grating will separate in different colors.

18.  When white light strikes a leaf, the leaf reflects light with a wavelength of 550 nm – green  The leaf absorbs all the other wavelengths  Colors may add or subtract  Additive primary colors = red, green and blue.  If mixed together they make white.  Subtracted primary colors - Reverse process  All three subtracted primary colors mixed together make black – the absence of color.

19. Refraction is the bending of the path of a light wave as it passes across the boundary separating two media. Refraction is caused by the change in speedcaused by the change in speed Index of Refraction: This is a ratio of how much faster light is in space compared to a specific medium. Index of Refraction (n) = speed of light in vacuum (air) speed of light in medium Formula: n = c v medium Chapter 15 Refraction

20. Medium n Velocity Space1.000003.00 x 10 8 m/s Air1.00029 Nail Polish Remover1.36 sugar soln. (30%)1.38 sugar soln. (80%)2.01 x 10 8 m/s crown glass1.52 calcite1.6583 sapphire1.77 diamond2.42 n is related to optical density of the material. Which substance is most dense?

21. SNELL’S LAW When waves travel from one medium to another that has a different velocity, they refract, or change direction.  The amount of that change is given by the equation: n 1 sin θ 1 = n 2 sin θ 2 All angles are measured to the Normal! Rays are refracted towards the normal if n i < n r n 1 faster n 2 slower θ2θ2 Air = n = 1.00 Water = n = 1.33

22. Draw and label Diagram If light enters a medium that is more at a perpendicular angle the light ray will not refract – only slow down or speed up

23. Fish appears closer to the cat than it really is Double refraction of Calcite

24. p. 583 Dispersion – incoming ‘white’ light of different wavelength is bent at different angles as it moves into a refracting material.  Index of refraction (n) is dependent on the frequency and wavelength – value for n decreases with increasing wavelength  Blue light (λ = 470 nm) bends more than red light (λ = 650 nm)  Shorter wavelengths of light (violet and blue) are slowed more and consequently experience more bending than red wavelengths (orange and red). http://www.micro.mag net.fsu.edu/primer/ligh tandcolor/refractionho me.html

25. Prisms disperse ‘white’ light into the ‘Visible Spectrum’ by refraction and dispersion of light

26.  Rainbows are created by dispersion and refraction of light in water droplets  Red on top of Rainbows

27. p. 604 Diffraction  Bending of waves around obstacles – or the spreading of waves by passing them through an aperture, or opening  light deviates or bends from a straight line path  Supports Wave Theory of light Diffraction Animation Interference of Light – p. 598  Light passed trough narrow slits produce a series of bright and dark parallel bands o Bright – constructive interference o maxima o Dark – destructive interference o minima

28. CD’s – example of interference and diffraction - Also the reflection of colors Interference Phenomena in Soap, plastics - Iridescence

29. Diffraction grating –Consists of many closely spaced narrow slits  Diffraction and interference to disperse light into its component colors –  Used in spectroscopes - chemical analysis of stars, and interstellar gases, structure of atoms and molecules.  Holograms – 3D impression of an object

30. Polarization – p 546  Light is a transverse wave vibrating in and out  Normal light vibrates in all directions  Polarization - the vibrations of light occur in a single plane Propagation of EM Waves Polarization of Light

31.  Light becomes polarized when it interacts with a substance that only allows it to vibrate in one plane.  Certain substances only allow light to pass through if it is vibrating in the proper direction.  The ability to polarize light depends on the molecular structure

32. Polaroid lenses reduce glare  Sunglasses Polarize Light vertically –  Reduces the glare given off of lakes/ocean/cars  Polarized lenses cut out the horizontal component.

33.  Polarized filters on cameras – better, clearer image  Polarization can be used to analyze substances, check for stress, and find weaknesses.

34. EM Waves are Transverse Waves

35. Dispersion of light