Color & Polarization and Refraction

1. Hannah Huether Mrs. Grayot, Physics, 6th Wave Project Color & Polarizationand Refraction

2. Color • Objects absorb certain wavelengths from the light that strikes them and reflects the rest of the light. • The object’s color depends on which wavelengths are absorbed and which are reflected • If an object reflects all incoming light it looks the color of the light

3. Characteristics • Objects with a specific color will absorb all wavelengths EXCEPT that color • Objects that don’t reflect light look black • Chlorophyll- primary pigment that gives leaves a green color • In the fall, this pigment is destroyed allowing other colors to be reflected by the leaves

4. Primary Colors

5. Additive vs Subtractive Combination of subtractive primary colors Combination of additive primary colors

6. Polarization • Linear Polarization- the alignment of electromagnetic waves in such a way that the vibrations of the electric fields in each of the waves are parallel to each other. • In an electromagnetic wave, the electric field is at right angles to both the magnetic field and the direction of propagation.

7. Unpolarized Light • Typical sources produce light that consists of waves that have electric fields oscillating in random directions • This light is considered unpolarized • Light can be linearly polarized through transmission • Unpolarized light can become linearly polarized when passed through certain crystals • The arrangement of molecules in the crystal determines the direction in which the electric fields are polarized

9. Transmission axis- line along which light is polarized for a substance that polarizes light by transmission • Only light waves that are linearly polarized along the transmission axis can freely pass through the substance • All light that is polarized at an angle of 90 degrees to the transmission axis does not pass through • The light is brightest when its plane of polarization is parallel to the transmission axis • Light can be polarized by reflection and scattering

11. When light is reflected at a certain angle from a surface, the reflected light is completely polarized parallel to the reflecting surface • Surface parallel to the ground- the light is polarized horizontally • Glaring light reflecting at a low angle from roads, bodies of water, and car hoods • Polarizing sunglasses filter out the glare caused by horizontal polarization by having a transmission axis oriented vertically.

12. When an unpolarizedbeam of sunlight strikes air molecules, the electrons in the molecules begin vibrating with the electric field of the incoming wave • Horizontally polarized waves are emitted by the electrons as a result of their horizontal motion • Vertically polarized waves are emitted parallel to the Earth as a result of their vertical motion

13. Refraction • Refraction- the bending of a wave front as the wave front passes between two substances in which the speed of the wave differs • Angle of refraction, Өr- Angle in between the refracted ray and the normal • Angle of incidence- Өi • Refraction occurs when light’s velocity changes • When light moves from one medium to another, some is reflected and some is refracted

14. When a light ray moves from air into glass, refracted part is bend TOWARD the normal • Light ray moving from glass to air is bent AWAY from the normal.

15. Characteristics • Examples of transparent media: Glass, ice, water, diamonds, and quartz • If the incident ray of light is parallel to the normal, then no refraction (bending) occurs • The frequency of the light does NOT change from one medium to another

16. Need to know • Index of refraction- the ratio of the speed of light in a vacuum to the speed of light in a given transparent medium • Index of Refraction: n=c/vindex of refraction=(speed of light in vacuum) divided by (speed of light in medium) • The index of refraction is a dimensionless number that is always greater than 1 since light always travels slower in a substance than in a vacuum • The larger the index of refraction is, the more refraction occurs.

17. Refraction causes objects to look like they are in different positions • Wavelength affects the index of refraction • The amount that light bends when entering a different medium depends on the wavelength of the light and the speed • A spectrum is produced when white light passes through a prism • Each color of light has a different wavelength and is refracted by a different amount

18. Snell’s Law • Willebrord Snell developed Snell’s Law in 1621 • Used to find the angle of refraction for light traveling between any two media • Snell’s Law: nisinӨi= nr sinӨrindex of refraction of first medium x sine of the angle of incidence = index of refraction of second medium x sine of the angle of refraction