1. Light

2. Light is a type of radiation which is emitted and detected by the retina of the eye.

3. Characteristics of Light Light comes to us in the form of Electromagnetic Waves What type of wave? --Transverse

4. It does not require a medium (matter) to travel through It travels in a straight line (these straight lines are called rays)

5. The electromagnetic Spectrum

6. Visible Light It is the range of frequencies of EM waves that stimulates the retina of the eye R-red700 nanometers(wl) O-orange Y-yellow G-Green B-Blue I-indigo V-violet400 nanometers (wl)

7. Transmission of Light Transparent-transmit light waves without distorting images (clear objects like glass & quartz) Translucent-transmit light waves but do not permit objects to be seen clearly through them (wax paper, frosted glass)

8. Opaque-transmit no light, but ABSORB or REFLECT all light incident upon them (ex, cloth, wood, cardboard) Light cannot travel through opaque materials (you can’t see through it)

9. Shadows-a shaded region that results when light falls on an object & thus cannot reach into the region on the far side of the object Total shadow-umbra Partial shadow-Penumbra

10. Theories of Light Newton thought that light consisted of particles Huygens thought that light consisted of waves Diffraction of light showed that light does bend, so waves But light moves in straight lines, so particles

11. Einstein used the photoelectric effect which showed that light was found in bundles of energy called photons. This led to the “dual nature of light”: it is both particles and waves

12. Speed of Light The speed of light was difficult to measure. The first measurement was done by Olaus Roemer He used the position of the moon and Jupiter in relation to the earth. The first accurate land measurement was by Michelson. His measurement was based on the reflection of light off a mirror.

13. Speed of Light Light travels at a certain speed through air The ‘speed of light’ is represented with the letter ‘c’ c = 3.0 x 108 m/s

14. Properties of Light Luminous -emits light waves (ex, sun, burning filaments in a light bulb) Illuminated -reflects light waves produced by an outside source (ex, moon)

15. Luminous flux-the rate at which visible light is emitted from a source; kind of like power (think flux~flows out ) Symbol-P Unit-lumen

16. Illuminance -rate at which light falls on a surface(rate at which it is illuminated) Symbol-E Unit-lux (lx)

17. Luminous intensity-How bright the light source is Intensity depends on: amount of light energy and how efficient the source is -Unit-candela (cd)

18. Polarization-only allowing a certain orientation of light to pass through a material. The aligning of vibrations in a transverse wave, usually by filtering out waves of other directions

19. Common light sources (light bulbs, fluorescent lamps, candles, etc) emit light not polarized since the vibrating electrons that produce light in these sources vibrates in random directions. When the light from these sources shine on a polarized filter, it will transmit light that is polarized.

21. PRACTICE: POLARIZATION Consider the three pairs of sunglasses. Which pair of glasses is capable of eliminating the glare from a road surface? Explain. (The polarization axes are shown by the straight lines.) SEE TRANSPARENCY EXAMPLE!