1. Light Introduction General Information

2. Light is a Wave Exactly as ocean waves, sound waves, slinky waves... Amplitude Wavelength Frequency Wave speed v = f

3. The speed of light is constant (in a given material) 3 x 10 8 m/s (186,000 miles per second) Nothing travels faster –Although light does slow as it enters a more dense medium Therefore, 3x10 8 m/s = f

4. So if v is constant... v = f As f goes up goes down As f goes down goes up Also E is related to amplitude –Big wave high energy (tsunami)

5. Light is different from most waves Because it does not need a medium to be transmitted –A water wave needs water –A sound wave needs air –A light wave needs nothing!

6. Light needs no medium because It is an electro-magnetic wave An electron moves –A changing electric field is produced –The electric field produces a magnetic field –The changing magnetic field produces an electric field –A changing electric field…

7. Moving at website http://www.phy.ntnu.edu.tw/java/emWave/emWave.html

8. Light is Electromagnetic Waves Only a small part are visible, most are not. The spectrum is organized by frequency and wavelength

9. All light is a wave Can only see visible light Can’t see the wave form We can see white light which is all colors together Gamma has high frequency small wavelength Radio has low frequency large wavelength

10. Energy is related to frequency As you increase frequency you increase energy As you decrease frequency you decrease energy Gamma high f, high E Radio low f, low E

11. High Energy Low Energy

12. Wait! In the wave unit we learned energy was proportional to amplitude –In a classic wave there is no connection between f and E Again, light is different from a traditional wave

13. Why is energy related to frequency for light not for other waves? We describe light as having a dual nature –We try to explain light in terms of human experience, but we can’t really describe it –Sometimes we notice light acts like a particle –Sometimes we notice light acting like a wave –Actually, light is both and neither.

14. Energy High frequency = high Energy Short wavelength = high Energy E = hf

16. What is more dangerous: Visible light or microwaves? How does a microwave work then? Why doesn’t it hurt us? Cell phones use microwaves

17. Intensity Brightness The number of light waves per area Nothing about the wave changes

18. We think of light as just brightness Really light is a SPECTRUM All wavelengths of light together creates white light –When a room is dark you see - black! Black is the absence of light –A prism separates the light into colors –But light is more than just the colors

19. Remember Light is electromagnetic radiation From gamma to radio waves Energy is proportional to frequency Light can be described as a wave and particle Otherwise, light behaves as any other wave