COLOR & POLARIZATIONAND REFRACTION

Hannah HuetherMrs. Grayot, Physics, 6th

Wave Project

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

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

Primary Colors

Additive vs Subtractive

Combination of additive primary colors

Combination of subtractive primary colors

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.

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

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

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.

When an unpolarized beam 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

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

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.

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

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.

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

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: ni sinӨi = nr sinӨr

index 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