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Maxwell’s Equations J. C. Maxwell developed 4 equations which govern all of electricity and magnetism. These 4 equations make light work. You do not need.

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Presentation on theme: "Maxwell’s Equations J. C. Maxwell developed 4 equations which govern all of electricity and magnetism. These 4 equations make light work. You do not need."— Presentation transcript:

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2 Maxwell’s Equations J. C. Maxwell developed 4 equations which govern all of electricity and magnetism. These 4 equations make light work. You do not need to know these.

3 Maxwell’s Equations

4 Spectrum Just like sound is classified according to its pitch, there are different kinds of light, classified by their frequency. The speed of light is constant.* Therefore, a certain frequency of light will always have the same wavelength. We can also classify light by wavelength.

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6 Electromagnetic Spectrum

7 Radio Lowest Frequency EM waves AM (up to ~1 MHz) FM (90~100 MHz) Shortwave (in between) VHF (TV) UHF (TV) Cell Phone reception Radar

8 Microwave (  -wave) The Gigahertz (GHz) range Wavelength in cm. Microwave ovens operate at 2.45 GHz This is a special frequency to cause resonance in water

9 Infrared (IR) Wavelength in “micrometers” (  m) Most commonly referred to as heat Hot objects radiate their thermal energy away. Up to a few hundred degrees, the radiant energy is in the IR range If we could see IR light, we would all shine brightly

10 More Infrared

11 Visible The light we can see A tiny portion of the EM spectrum Red ( = 700 nm) Orange Yellow Green Blue Indigo Violet ( = 450 nm)

12 Ultraviolet (UV) Wavelength as low as 10 nm Used to kill germs Black Lights The part of sunlight that causes sunburn and skin cancer Partially blocked by the ozone layer

13 X-Ray These can be useful, but also dangerous Wavelength between 10 nm and 10 pm That is from 10 billionths of a meter to 10 trillionths of a meter

14 Gamma Ray (  ray) < 10 pm High energy Dangerous Remember Gamma radiation from last semester

15 Practice What is the wavelength of AM radio wave 960 kHz? f = 960,000 Hz c = 3 × 10 8 m/s = c/f = 3 × 10 8 m/s ÷ 960,000 Hz = 312 m

16 Practice What is the frequency of a “shortwave” radio wave 120 meters long? = 120 m c = 3 × 10 8 m/s f = c/ f = 3 × 10 8 m/s ÷ 120 m f = 2,500,000 Hz = 2,500 kHz = 2.5 MHz

17 Practice What is the wavelength of an FM radio wave? These waves are approximately 100 MHz (100 × 10 6 Hz). f = 100,000,000 Hz c = 3 × 10 8 m/s = c/f = 3 × 10 8 m/s ÷ 100,000,000 Hz = 3 m

18 Practice What is the wavelength of a microwave in a microwave oven? These waves are 2.45 GHz (2.45 × 10 9 Hz). f = 2,450,000,000 Hz c = 3 × 10 8 m/s = c/f = 3 × 10 8 m/s ÷ 2,450,000,000 Hz = 0.12 m = 12 cm

19 Conclusion -- Quiz Wed. (4/29) Electromagnetic Spectrum Radio Microwave Infrared Visible Roy G Biv Ultraviolet X Ray Gamma Ray Visible Spectrum Red Orange Yellow Green Blue Indigo Violet

20 Assignment Chapter 12 vocabulary


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