Mirrors Chapter 13 - 15

Chapter 13 Section 2 & 3

Mirror History Mirrors are the oldest optical instruments Almost 4000 years ago, Egyptians used polished metal mirrors Sharp, well-defined reflected images became possible in 1857, when Jean Foucault developed a method for coating glass with silver

Plane mirror Light rays are reflected with equal angles of incidence and reflection Bathroom mirrors Object- a source of diverging (spreading) light rays Every point on the object is a source of diverging light May be luminous, more commonly illuminated

Image What you see- brains thinks the light comes from the image Virtual image- an image where the light rays do not actually converge on the point In a bathroom mirror- where do you see the image? Is that where you really are?

Example- On board If the image and the object are pointing in the same direction, the image is called an erect image In a plane mirror- the image formed is the same size as the object and is the same distance behind the mirror as the object is in front. If you wave your right hand it looks like the left hand is moving

Concave mirrors Reflects light from the inner surface Inside a spoon The surface of a concave mirror reflects light to a given point called the focal point (F) The distance from the focal point to the mirror along the principal axis is the focal length (f)

Concave The concave mirror is used whenever a magnified image of an object is needed Dressing-table mirror The radius of curvature is the same as the radius of the spherical shell of which the mirror is part. Therefore the distance from the mirror’s surface to the center of curvature C is the radius.

Features of an image Can be found using formulas, and will tell you if the image is: Real or virtual Inverted or right side up Magnified or reduced

Formula symbols di is image distance do is object distance hi is image height ho is object height f is the focal length (1/2 the radius) C is the center of curvature (2f or radius)

Equations On board Page 457, 458 Assignment – page 462 (1-2) 1/do + 1/di = 1/f M = hi/ho = - di / do Page 457, 458 Assignment – page 462 (1-2)

Convex Mirrors A spherical mirror that reflects light from its outer surface Rays reflected from a convex mirror always diverge, so they do not form real images Form reduced images, and reflect a larger area of view

Assignment Page 466 (1-2)

Chapter 14 Section 2

Lenses A lens is transparent with a refractive index larger than air Convex lens- thicker at the center Are converging lenses; refract parallel light rays so that the rays meet Concave lens- thinner in the middle Diverging lens; the rays passing through are spread out

Lens/Mirror Equation f is positive for convex lenses and negative for concave lenses do is positive on the object side of the lens di is positive on the image side, where images are real di is negative on the object side of the lens where images are virtual

Equations The lens/Mirror equation can be used to find the location of an image The magnification equation can be used to find the image size Assignment- Page 501 (1 & 4)

How do eye glasses Work? How do you think eye glasses work? How do microscopes and telescopes work? What about a camera? Write your hypothesis/explanation for each. Read Page 502-505 Were you right or wrong?

Why are the edges of shadows not sharp? Grimaldi named the slight spreading of light around barriers diffraction Thomas Young developed an experiment that allowed him to make a precise measurement of light’s wavelength using diffraction

Young’s Double-Slit Experiment Young directed a beam of light at two closely spaced narrow slits in a barrier The light was diffracted, and the rays from the two slits overlapped. When the overlapping light beams fell on a screen a pattern of bright and dark bands was produced

Measuring the wavelength of light Young used the double-slit experiment to make the first precise measurement of the wavelength of light λ = (xd) / L x = the separation between the central bright line and the first-order bright line L= distance between slit & screen d = distance between the two slits

Diffraction Gratings Transmits or reflects light and forms an interference pattern in the same way that a double-slit does Wavelength using a Diffraction Grating λ = (xd)/L = d sin θ

Assignment Page 531 (1) Page 538 (1 & 2)

Lasers