1. Light & Waves Mrs. Wolfe

2. Recall that Light is Defined by Wavelength The Electromagnetic Spectrum Where does light come from? Electrons jumping Space Gamma Radiation

3. Electromagnetic Spectrum The light we can see is called Visible light. But the spectrum includes mostly light that we can’t see… For example, the sun gives us other “rays.” Like what?

5. Gamma Rays Emitted by radioactive substances Most dangerous types of EM waves Why?? Highest Energy/Frequency

6. X-rays Also emitted by unstable, radioactive atoms Penetrate through flesh but not bone, so they’re useful in medicine. Prolonged exposure can cause damage to body tissues. Why??

7. Ultra-violet rays Primarily from the sun Produces Vitamin D in human skin..so it’s GOOD! Causes darkening of the skin Overexposure causes sunburn and can burn the retina of the eye Used to sterilize things

8. Visible Light White light Only light the human eye can see Wavelengths range from: 4 x 10 -7 to 7 x 10 -7 meters Each wavelength is a certain color R.O.Y. G. B.I.V. Red – longest wavelength Violet – shortest wavelength

9. The Visible Light Spectrum

11. Infra-red rays Emitted by all objects “Heat waves” Hotter objects emit more waves than cooler objects Infra-red waves can penetrate darkness, clouds, mist, etc. Used in military Used in your remote controls

12. Microwaves Most easily absorbed by water in food. When that happens, heat is produced. That’s how we cook our food…by energizing the food with “invisible” light!

13. Radio Waves Used in TVs and radios Police radio communication Navigation systems

14. How can I prove that these invisible light rays exist? Time for a Demo! Michael Faraday –Great electricity scientist –1791-1867 The Faraday Cage!

15. Energy and Light Some types of light have more energy than others. Which has more energy – Gamma rays or Microwaves? Which has less energy – orange light or green light?

16. Practice Problem Plants use energy from sunlight to make their food during photosynthesis. A packet of light energy, a photon, is changed into food. Which would make a better grow-light: red or violet light? Wavelength (nm) % ABS

17. Why can’t we see all the light? We have rods and cones in our eyes that can only detect certain wavelengths of light. Other animals see different wavelengths. Snakes, for example, see infrared light.

18. Go to http://science.howstuffworks.com/eye2.htm Scroll down and watch the video! http://science.howstuffworks.com/eye2.htm

19. A few last words on light Light can travel through a vacuum. Example? Space! All light travels at the same speed…3 x 10 8 m/s in a vacuum! That’s REALLY fast!

20. Practice Problem What is the wavelength of light has a frequency of 0.75 x 10 15 ? S = f x w S = 3 x 10 8 m/s, F=0.75 x 10 15 Hz 3 x 10 8 m/s = 0.75 x 10 15 Hz x W W= 4 x 10 7 m What color is this? Violet!!

21. Take Home Messages Each type of light has its own wavelength, frequency, and energy. Visible light is the only light we can see. ROY G BIV (longest to shortest wavelength) Light can travel through a vacuum! The speed of light is CONSTANT (3 x 10 8 m). Can you use the calculator to solve math problems for frequency, wavelength, and speed?