# Light Chapter 16-19.

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Light Chapter 16-19

Chapter 16 Section 2: Wave Nature of Light
Grimaldi recognized the phenomenon that light bends around a barrier- diffraction. Christian Huygen used the wave model to explain diffraction All points of a wave front of light can be thought of as smaller waves. The crest of each wave can be thought of as a series of point sources. Each point source creates a circular wavelet. All the wavelets combine to make a flat wave front, except at the edge where circular wavelets move away from the wave front. Draw picture. Phet. So the small slit creates the best diffraction; where the waves break up into the color spectrum. The red wave(longer wavelength being farthest away from the white light because it creates the largest angle

Color Newton performed experiments on color when a narrow beam of sunlight passes through a glass prism. An ordered arrangement of colors occur- spectrum. Grimaldi and Newton together proved light has wave properties and each color of light is associated with a wavelength.

Light/ Color cont’d Visible Light falls within the range of 400 nm to 700 nm. The longest wavelength being red and the shortest being violet ROYGBIV

Primary colors – red, green and blue Secondary colors- cyan, yellow and magenta Combination of all colors – white Complimentary Colors- are two colors of light that can combine to make white light. Yellow is complimentary to blue Red is complimentary to cyan Magenta is complimentary to green This is why yellowish laundry can be whitened with a bluing agent added to detergent

Color by Subtraction/ Light
Objects can absorb and reflect light A dye contains molecules that absorb certain wavelengths of light and transmit or reflect others. When light is absorbed, its energy is taken into the object that it strikes and is turned into other forms of energy. A red shirt is red because dyes reflect red light to our eyes

Color by Subtraction cont’d
Primary pigment(crushed minerals)- absorb only one primary color and reflect two from white light. These are yellow, cyan and magenta. Secondary pigment- absorb two primary colors and reflect one . These are red, green and blue.

Color

Polarization of Light Polarization is the production of light in a single plane of polarization Ordinary light actually contains waves vibrating in every direction perpendicular to its direction of travel. If a polarizing medium is placed in a beam of ordinary light, only the components of the waves in the same direction as the polarizing axis can pass through. Example sunglasses, polarizing filters in camera lenses

Polarization of light

Chapter 18: Refraction of Light
The path of travel of light bends when it passes from a medium with an index of refraction of n1, into a medium with a different index of refraction, n2. Snell’s Law: n1sinΘ = n2 sinΘ The ratio of the speed of light in a vacuum,c, to the speed of light in any medium, v, is the index of refraction, n, of the medium. n = c/v

Refraction of Light cont’d
When light traveling through a medium hits a boundary of a medium with a smaller index of refraction, if the angle of incidence exceeds the critical angle Θc, the light will be reflected back into the original medium by total internal reflection. sin Θc = n2 / n1

Chapter 18 Section 2: Diffraction (more)
The cutting of coherent light on two edges spaced closely together produces a diffraction pattern, which is a pattern on a screen of constructive and destructive interference.

Single Slit Diffraction
If a small opening that is larger than the wavelength of the light being transmitted is shined through a single slight then the light will be diffracted by both edges. Bright and dark bands will appear o the screen.

Double Slit Experiment
Young devised this experiment, which lead to a formula used determine wavelengths of light. It also proved that light has wave properties. He produced an interference pattern by shining light from a single coherent source through two slits. Young directed coherent light at 2 closely spaced, narrow slits in a barrier. When the overlapping light from the two slits fell on the observing screen, the overlap didn’t produce even illumination but instead created a pattern of bright and dark bands that he called Interference fringes. These resulted from constructive and destructive interference.

Double slit experiment cont’d
What occurs: Monochromatic light- one wavelength; in constructive interference a bright central band of color on screen and other bands after it are equal in space and length, their intensity decreases the further away from the central band Between bright bands are dark areas of destructive interference( the positions of these depend on the wavelength of the light) When white light is used the construct. Interfer. Colored spectra occur instead of dark and bright bands. In the central band all wavelengths interfere construct. So it is white.

Young’s Double Slit Experiment
The interference occurs because each point on the screen is not the same distance from both slits. Depending on the path length difference, the wave can interfere constructively (bright spot) or destructively (dark spot). The Wave Nature of Light 24

Young’s Double Slit Experiment
Bright q x L S1 d Constructive Interference S2 screen The Wave Nature of Light 24