24.1 The Electromagnetic Spectrum

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. About Electromagnetic Waves • 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. The Electromagnetic Spectrum • 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