1. 24.1 The Electromagnetic Spectrum pp. 522 - 527 Mr. Richter

2. Agenda  Warm Up  Review HW  Notes:  About Electromagnetic Waves  The Electromagnetic Spectrum  Low-Energy EM Waves  Visible Light  High-Energy EM Waves

3. Objectives: We Will Be Able To…  Learn the relationship among the frequency, wavelength and energy of light.  Identify the different kinds of electromagnetic waves, and rank them in order of energy.

4. Warm-Up:  To read your book, you move 6 times closer to the lamp than you were before.  How much brighter does the light appear to be on the page of the book?

5. About Electromagnetic Waves

6.  Electromagnetic (EM) waves are formed when moving electrons change the electric and magnetic fields around them.  Like a hand shaking a magnet.  Sources of EM waves emit oscillating electric and magnetic energy.  Obviously, EM waves are non-mechanical waves.

7. The Electromagnetic Spectrum

8.  There is a wide range of frequencies of EM waves called the electromagnetic spectrum.  Remember, low frequency means:  Low energy  Long wavelength

9. The Electromagnetic Spectrum  The EM spectrum contains seven types of waves, in order from low to high frequency:  radio  microwaves  infrared  visible light  ultraviolet light  x-rays  gamma rays  All of the spectrum is invisible to us except for visible light.  Just like there are some sounds we can’t hear.

10. The Electromagnetic Spectrum  The EM spectrum contains seven types of waves, in order from low to high frequency:  radio  microwaves  infrared  visible light  ultraviolet light  x-rays  gamma rays  The EM spectrum is broken up into two halves: low- energy and high-energy.  High-energy waves can remove an electron from an atom (= radiation = dangerous!)  Low-energy waves cannot.

11. Low-Energy EM Waves: Radio and Microwaves  Radio waves are the lowest- frequency waves.  Wavelengths can be kilometers long!  Microwaves  Used by cell phone and microwave ovens  Microwave ovens are tuned to the natural frequency of water molecules. (Resonance!)

12. Low-Energy EM Waves: Infrared  Infrared waves are just below the frequency of visible light.  They are sometimes referred to as radiant heat.  Although we can’t see them, we can feel them.  We have designed electronic equipment to help us see them.

13. Low-Energy EM Waves: Visible Light  Visible light makes up a very small portion of the EM spectrum.  Wavelengths range only from about 400 – 700 nanometers.  Not much bigger than individual atoms.  Red: long wavelength, low frequency  Violet: short wavelength, high frequency.

14. High-Energy EM Waves  Ultraviolet light  Easily absorbed by humans. We need some, but not too much.  X-rays  Pass easily through skin, but not through bones. Dangerous in large amounts.  Gamma rays have the highest frequency.  Lots of energy!  They can completely push electrons out of an atom!

15. Wrap-Up: Did we meet our objectives?  Learn the relationship among the frequency, wavelength and energy of light.  Identify the different kinds of electromagnetic waves, and rank them in order of energy.

16. Homework  p. 527 #1, 2, 4, 5