Let there be ... Light

Two theories could explain The Nature of Light What is Light? By the 17th century, light had been observed to… 1. travel in straight lines 2. reflect 3. refract 4. transmit energy from one place to another Two theories could explain these phenomena.

The WAVE THEORY, advocated by Christian Huygens and Robert Hooke, said that light was a wave. The PARTICLE (corpuscular) THEORY, advocated by Isaac Newton and later by Pierre Laplace, said that light was made up of a stream of tiny particles called corpuscles.

Light is ... This leads us to the Duality Principle: a wave when it acts like a wave a particle when it acts like a particle

Visible light is that portion of the electromagnetic spectrum which stimulates the retina of the human eye. Visible spectrum wavelengths range from about 400 nm (violet) to 760 nm (red). Light travels at about 3 x 108 m/s through empty space and slightly slower through air. Remember that for all waves, v = f.

COLOR can clearly see objects through them Materials may be classified as: transparent - readily transmits light; can clearly see objects through them translucent - transmits, but diffuses, light; cannot see objects clearly through them opaque - transmits no light; cannot see through them

WHITE light is composed of all colors. Red, orange, yellow, green, blue, violet is the order of increasing frequency or decreasing wavelength. Frequencies directly above this spectrum are ultraviolet. Frequencies directly below this spectrum are infrared.

The color of an opaque object depends on the colors (frequencies) of light incident upon it and on the colors (frequencies) of light reflected. The color of a transparent object depends on the colors (frequencies) of light incident upon it and on the colors (frequencies) of light transmitted.

colors that combine to form white light. Complimentary colors are two colors that combine to form white light. Red and cyan, blue and yellow, green and magenta are pairs of complimentary colors. Red, blue, and green are called primary colors or secondary pigments. Cyan, yellow, and magenta are called primary pigments or secondary colors.

POLARIZATION Only transverse waves may become polarized.

air water As light reaches the boundary between two media, its energy is partially reflected back and partially transmitted into the new medium. The amount that is reflected depends on the types of materials and the angle of incident rays. air water

Laws of Reflection First Law Second Law The angle of incidence, i, is equal to the angle of reflection, r. n i r Second Law The incident and reflected rays, and the normal, are coplanar.

Images formed by mirrors and lenses may be classified as real or virtual. Real Image formed by actual rays of converging light Virtual Image not formed by actual rays of converging light, but from where the rays of light appear to come (diverging light rays)

Plane Mirror Images 1. virtual 2. upright 3. same size as object Images formed by plane mirrors are always: 1. virtual (virtual images are always behind mirrors) 2. upright (virtual images are always upright) 3. same size as object (if the image is larger or smaller, the mirror isn’t flat) 4. front and back are reversed (some say “left and right”) 5. located as far behind the mirror as the object is in front

Curved Mirrors Terminology center of curvature - C; the center of the original sphere radius of curvature - r; distance from center of curvature to the mirror vertex - V; the center of the mirror principal axis - a line through C and V principal focus - F; the point on the principal axis where light rays parallel and close to the principal axis converge; or from where they appear to diverge focal length - f; distance from V to F

Ray Diagrams Concave (Converging) Mirrors rays parallel and close to the principal axis reflect through the focus 2. rays passing through the focus reflect parallel to the principal axis 3. rays passing through the center of curvature reflect straight back along the incident path C F

Convex (Diverging) Mirrors 1. rays parallel and close to the principal axis reflect away from the focus 2. rays heading toward the principal focus reflect parallel to the principal axis 3. rays heading toward the center of curvature reflect straight back along the incident path F C

di/do = si/so 1/f = 1/do + 1/di Mirror Equation Magnification Diverging rays must be extended as dotted lines behind the mirror in order to locate some images. Mirror Equation Magnification di/do = si/so 1/f = 1/do + 1/di f = focal length; positive for converging mirrors, negative for diverging mirrors do = object distance; usually positive di = image distance; can be positive or negative so = object size (height) si = image size (height)

Images formed by concave (converging) mirrors may be: 1. real, virtual, or non-existent 2. upright or inverted 3. reduced, enlarged, or same size 4. in front or behind the mirror The image properties depend on the object’s location with respect to the mirror, focus, and center of curvature.

object is beyond the center of curvature: image is real, inverted, and reduced object is on the center of curvature: image is real, inverted, and the same size object between center of curv. and focus: image is real, inverted, and enlarged object is on the focus: no image; rays reflect parallel object is inside the focus: image is virtual, upright, and enlarged

4. located behind the mirror between the vertex and focus Images formed by convex (diverging) mirrors are always: 1. virtual 2. upright 3. reduced 4. located behind the mirror between the vertex and focus

General Image Trends real images are always inverted virtual images are always upright real images are always in front of the mirror virtual images are always behind the mirror negative image distance means virtual image positive image distance means real image