1. Physics Mrs. Coyle

2. Electromagnetic Waves: oscillating electric and magnetic fields. http://www.physchem.co.za/OB12-ele/Graphics/wavetrain.gif

3. Electromagnetic Waves Do not require a medium. Can travel through space (vacuum). Ex.: Light from the sun reaches us. Transverse

4. Electromagnetic Waves Type of radiation Wavelengths(m) Radio 570 - 2.8 TV5.6 - 0.34 Microwave0.1 - 0.001 Infrared radiation10 -3 - 10 -7 Visible Light 700x10 -9 - 400x10 -9 Ultraviolet10 -7 - 10 -10 X-rays10 -10 -10 -12 Gamma raysshorter than 10 -12

5. Visible Light is detected by the human eye. red700 x 10 -9 (700nm) orange yellow green 550 x 10 -9 blue indigo violet 400 x 10 -9 (400nm)

6. Electromagnetic Spectrum

8. Speed of Light, c All EM waves have a speed through vacuum of 3 x 10 8 m/sec. c= f λ

9. Problem If a light wave’s frequency is 5.45 x10 14 Hz, what is its wavelength? What color light is it? Answer: 550x 10 -9 m, green

10. Calculating the Speed of Light Danish Astronomer, Ole Roemer (~1668) found that the period of the moon of Jupiter, Io, varied depending on the location of the Earth. Distances were known. Estimated speed of light: 2.2 x10 8 m/s

11. Albert Michelson, American (1880’s) Measured time for light to make a round trip in California mountains 35km apart. Measured speed of light: 2.997996 x10 8 m/s First American to win Nobel prize.

12. Speed of Light (1983) Seventeenth General Congress on Weights and Measures measured: 2.99792458 x 10 8 m/s We round to 3 x 10 8 m/s

13. Luminous Objects emit light. Illuminated Objects reflect light rays.

14. Luminous Flux, P Rate at which light is emitted from a source. Unit: lumen, lm

15. Illuminance, E, measures illumination of a surface. E = (Luminous flux P) (area around source) E= P / (4πd 2 ) d : distance from source Unit: Lumens/ m 2 =lux=lx

16. Problem A lamp is moved from 20cm to 40cm from a book. Compare the illumination before and after.

17. Candela (candle power) Luminous intensity of a point source is the luminous flux that falls on 1m 2 of a sphere of 1 m radius. cd = Luminous flux/π One of the fundamental SI units