1. LIGHT

2. Key Points for today What are E-M Waves? Where does light fit in to all of this? Comparing λ and f for different E-M waves Reading quiz next day (16.1)

3. Just another wave……. Albeit a special kind of wave! Light is an ________________ wave. This means that no medium (water, air, your desk) is needed for the wave to travel.

4. Albert Einstein

5. LIGHT: What Is It? Light Energy –Atoms As atoms absorb energy, electrons jump out to a higher energy level. Electrons release light when falling down to the lower energy level. –Photons - bundles/packets of energy released when the electrons fall. Light: Stream of Photons © 2000 Microsoft Clip Gallery

6. Transverse Waves Energy is perpendicular to direction of motion Moving photon creates electric & magnetic field –Light has BOTH Electric & Magnetic fields at right angles! © 2000 Microsoft Clip Gallery

7. Electromagnetic (E-M) Waves The light we see is only a small part of the E-M spectrum

8. Electromagnetic Spectrum © 2000 Microsoft Clip Gallery

9. Electromagnetic Spectrum Visible Spectrum – Light we can see –Roy G. Biv – Acronym for Red, Orange, Yellow, Green, Blue, Indigo, & Violet. –Largest to Smallest Wavelength.

10. Questions How long are Radio waves? (give a range) –This distance is approximately equal to _____ –These E-M waves have more / less energy than X-Rays

11. Electromagnetic Spectrum Invisible Spectrum –Radio Waves Def. – Longest wavelength & lowest frequency. Uses – Radio & T.V. broadcasting. © 2000 Microsoft Clip Gallery

12. Modulating Radio Waves Modulation - variation of amplitude or frequency when waves are broadcast –AM – amplitude modulation Carries audio for T.V. Broadcasts Longer wavelength so can bend around hills –FM – frequency modulation Carries video for T.V. Broadcasts © 2000 Microsoft Clip Gallery

13. Electromagnetic Spectrum Invisible Spectrum (Cont.) –X-Rays Def. - EM waves that are shorter than UV rays. Uses: Medicine – Bones absorb x-rays; soft tissue does not. Lead absorbs X-rays.

14. Electromagnetic Spectrum Invisible spectrum (cont.) –Gamma rays Def. Highest frequency EM waves; Shortest wavelength. They come from outer space. Uses: cancer treatment.

15. LIGHT: Particles or Waves? Wave Model of Light –Explains most properties of light Particle Theory of Light –Photoelectric Effect – Photons of light produce free electrons © 2000 Microsoft Clip Gallery

16. Intro to Velocity To find out how fast an object is moving, we need two things: 1.Distance 2.Time velocity = distance/time v = d/t

17. Man….those things move fast (Pg. 331) How far is it across Earth’s orbit? How much time does it take light to travel across Earth’s orbit?

18. TO DO….. Read P. 330 – 336 Do “Notes on Light” – Page 1 Do: Practice Problems (1 - 10) in Chapter 16