1 / 17

Physics Mrs. Coyle

Light. Physics Mrs. Coyle. Electromagnetic Waves: oscillating electric and magnetic fields. http://www.physchem.co.za/OB12-ele/Graphics/wavetrain.gif. Electromagnetic Waves. Do not require a medium. Can travel through space (vacuum). Ex.: Light from the sun reaches us. Transverse.

africa
Download Presentation

Physics Mrs. Coyle

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Light PhysicsMrs. Coyle

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

  3. ElectromagneticWaves • 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 TV 5.6 - 0.34 Microwave 0.1 - 0.001 Infrared radiation 10-3 - 10-7 Visible Light 700x10-9 -400x10-9 Ultraviolet 10-7 - 10-10 X-rays 10-10 -10-12 Gamma rays shorter than 10-12

  5. Visible Light is detected by the human eye. red 700 x 10-9 (700nm) orange yellow green 550 x 10-9 blue indigo violet400 x 10-9 (400nm)

  6. Electromagnetic Spectrum

  7. Speed of Light, c • All EM waves have a speed through vacuum of 3 x 108 m/sec. c= f λ

  8. 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

  9. 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 x108 m/s

  10. 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 x108 m/s • First American to win Nobel prize.

  11. Speed of Light (1983) Seventeenth General Congress on Weights and Measures measured: 2.99792458 x 108 m/s We round to 3 x 10 8 m/s

  12. Luminous Objectsemit light. Illuminated Objectsreflect light rays.

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

  14. Illuminance, E, measures illumination of a surface. E = (Luminous flux P) (area around source) E= P / (4πd2 ) d : distance from source • Unit: Lumens/ m2=lux=lx

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

  16. Candela (candle power) • Luminous intensity of a point source is the luminous flux that falls on 1m2 of a sphere of 1 m radius. • cd = Luminous flux/π • One of the fundamental SI units

More Related