l. Refraction of Light A. Refraction is the bending of light at the boundary of two media. 1. It is caused by differences in the way light travels in the two media a) Light changes speed unequally. (1) One side of the light becomes slower/faster 2. If light is perpendicular to the new medium, light will not refract a) If the media have the same index of refraction, light will not refract B. Index of Refraction 1.
How well light travels through a medium is measured by its index of refraction a) Larger the index the slower light travels . N = C/v where N is the index of refraction C is the speed of light in a vacuum and V is the speed of light in the medium. A) N has no label and speeds are in m/s C. Refraction is what causes object to appear in different locations when the light from the object goes between media 1 . Refraction depends upon wavelength. A) Smaller the wavelength, the more refraction 2. The difference in the amount of bend between polychromatic light causes a spectrum to appear D.
Kennel’s Law 1. In Sinai = Nursing a) Where In -?index of refraction of the incident material (original medium) b) IQ = the Engle of incidence c) In -?index of refraction of the refracting material (final medium) d) car = the angle of refraction II. Thin Lenses A. Concave vs.. Convex 1 . Concave a) Diverging lens- light bends away from a point. B) Negative focal length c) Thick at edges and thin in the middle d) Always creates virtual, reduced, upright images B. Convex 1 . Converging lens- light bends towards a point. ) Positive focal length b) Thick in middle and thin at the edges c) Can create real or virtual; enlarged, same size, or reduced; or inverted or upright images. D) No image also possible C. Lens Equation 1. L/f=l/p+l/q (same as mirror) a) Where f = focal length b) positive for convex and negative for concave c) p -?object distance d) q = image distance D. Magnification 2. Where M = magnification (no label) 3. P -?object distance 4. Q = image distance 5. H’ = height of image 6. H = height of object E. Structure of the Eye 1. The main parts of the eye are the cornea, pupil and iris, lens, and the retina. 2.
The cornea is the transparent, outer coating of the eye a) Helps focus light entering eye 3. The pupil allows light rays to enter eye 4. The iris is the color part of eye ) Controls the amount of light that enters eye (1) Regulated by signals from brain F. The lens is a sealed capsule containing a clear fluid 1. Focuses light onto sensor cells on the back of eye G. The retina is the inner surface of the eye where reflected light is collected 1. Covered by nerve endings called rods and cones which convert light into electrical signals sent to the brain through the optic nerve H. Correcting Vision Problems 1 .
Myopia (Nearsightedness): causes distant objects to appear blurry a) Occurs because the cornea is too curved or eye ball is too long b) Can see nearby objects Leary c) Can be corrected by placing a diverging (concave) lens in front of eye d) Some cases of this can now be treated with surgery l. Hyperemia (Farsightedness): causes nearby objects to appear blurry 1 . Caused by either cornea not curved enough or short eye ball a) Can see distant objects clearly b) Usually corrected by placing a converging (convex) lens in front of the eye J. Astigmatism: objects at any distance appear blurry 1.
The cornea or lens is misshapen 2. Lens has two different focal points, causing distortion or blurring of images 3. Corrected with specialized eyeglass lens shapes K. Eyeglass lens are usually Concave lens 1 . The different focal lengths are used to move the image forward or backwards 2. Used to move the image onto the retina L. Contact lens use different index of refraction to move the light to create on image on the retina M. Combined Lenses 1 . When lenses are used together, the image of the first lens becomes the object of the second lens. N. Microscopes use two converging lenses 1 .
The objective lens (nearest the object) with a short focal length and an eyepiece lens with a longer focal length O. Telescopes use two converging lenses 1 . Same as microscope, but overlapping focal lengths P. Dispersion-the separation of light into a spectrum by refraction 1. Light waves of different wavelengths have slightly different refractive indices 2. Red light has smallest index of refraction violet has largest Q. Because different colors have different refracting angles, when white light falls on a prism red light is bent the least spectrum R. Newton investigated dispersion 1. Proved prisms don’t add colors to light Ill.
Materials that disperse light 1. Glass 2. Diamonds B. Water-rainbows are sunlight dispersed by water droplets in the atmosphere C. RAINBOWS 1 . Sunlight is refracted off the front and back of the water droplet and produces a complete spectrum. 2. Depending on the angle of the sun, droplet, and observer particles seem to only have one color. A) That’s why we see the different bands of color in the sky. Red has 420 angle with sun’s rays while blue is at a 400 angle IV. Optical Phenomena A. Total Internal Reflection 1 . When light tries to enter a less optically dense material, the light might refract 900 or more. ) This will bend the light between the two media or back into the original material. 2. The refraction of light of 900 (between the two media) is caused by a special angle of incidence -the critical angle 3. The bending of light back into the original medium (refraction > 900) is known as total internal refraction B. Conditions for Total Internal Reflection 1 . Light must move from a higher index of refraction to a lower index of refraction 2. Light must bend away 3. Light must be greater than the critical angle C. Dispersion of Light 1. Light travels at 3. 00 x 108 m/s only through a vacuum of space but in other media, light moves slower