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Light

Light. Electromagnetic waves are generated by accelerating electric charges. The electromagnetic spectrum consists of many different wavelengths with varying energies. Light.

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Light

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  1. Light • Electromagnetic waves are generated by accelerating electric charges. • The electromagnetic spectrum consists of many different wavelengths with varying energies.

  2. Light • A small portion of the electromagnetic spectrum stimulates the human retina, and is referred to as light. (page 288).

  3. Light • Light travels in straight lines. A small beam of light consists of many waves travelling together. • A line representing the direction of light wave travel is called a ray.

  4. Light • All electromagnetic radiation travels at the same speed in a vacuum. (3x108m/s) • In material media electromagnetic waves with different frequencies travel at different speeds.

  5. Light • Around 1676 an astronomer named Roemer estimated the speed of light using variations in the duration of eclipses of one of Jupiter’s moons. • (Page 289)

  6. Light • In 1879 an American physicist named Albert Michelson measured the speed of light accurately using a rotating mirror. (Page289)

  7. Light • Some materials such as glass transmit light. These materials are called transparent materials. • Translucent materials transmit light, but objects cannot be seen through them clearly.(frosted glass) • Opaque materials absorb or reflect all light that falls on them. (metal)

  8. Light • A luminous body emits light waves. • An illuminated body reflects light waves. • Luminous intensity is the amount of light that a body gives off.

  9. Light • Luminous intensity(I) is measured by comparing it with an international unit the candela (cd). (Page 290) • The rate at which light energy is emitted from a sourceis named the luminous flux. It’s unit is the lumen. • A one candela source emits 4πlumens.

  10. Light • The rate at which light energy falls on a unit area a certain distance from the source is illuminance, E. • On lumen per square meter =1 lux (lx)

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