Pre-historic man saw his image reflected to him in water Ancient Egyptians used polished metals to see their images In 1857, Jean Foucault developed a method of coating glass with silver – letting people see a clean, clear image of himself.
A flat, smooth surface that reflects light through regular reflection –Angle of incidence equals angle of reflection Plane Mirrors object image
Plane Mirrors ObjectImage Virtual Image d O = d i h O = h i Erect Image
Early Work – Mar. 30 List the three rays to follow to find an image.
Early Work – Apr. 3 How can you tell if an image is real or virtual? $2…
Concave Mirror Review Principal Axis – line perpendicular to center of mirror Focal Point – point where rays converge or diverge to Center of curvature (or radius) = 2F Focal length – distance from focal point to mirror, f 2f = r
Real v. Virtual Real image – rays that converge on a single point and that image can be displayed on a screen –Looking for if rays actually converge at the point Virtual image – image formed without rays converging on point
Real Images Concave mirrors can form real images – when object is past C –Three rays to follow One parallel One through focal point One to center of mirror
Image Equations Magnification – ratio of size of image to size or object
Describing a Real Image Mathematically – –If h i is negative, the image is inverted –If d i is positive, the image is real
Example A concave mirror has a radius of curvature of 20.0 cm. An object, 2.0 cm high, is placed 30.0 cm from the mirror. –Where is the image located? –How high is the image?
Virtual Images Concave mirrors can form virtual images – when object between F and mirror –Three rays to follow One parallel One through focal point One to center of mirror
Example An object, 2.0 cm high, is placed 5.0 cm in front f a concave mirror with a focal length of 10.0 cm. How large is the image, and where is it located?
Early Work – Apr. 9 Draw the image formed by an object and a convex mirror. Describe the image (3).
Spherical Aberration When we draw rays, have them reflect off perpendicular plane rather than curved mirror –Equations even follow this But real rays reflect off curved surface so only rays close to principal axis reflect through the focus
Lens History Eyeglasses – 13 th century 1610 – Galileo made telescope –Observed moons of Jupiter Since –Microscopes –Cameras –Solar Powered Marshmallow Roasters Probably most useful optical device
Types of Lenses Lens – transparent material with index of refraction larger than that of air –Faces can be concave, convex, or plane –Convex Lens – thicker in middle. Converging lens because light rays converge to one point on other side. –Concave Lens – thinner in middle. Diverging lens because light rays spread out on other side.
Convex Lenses Light refracts at both surfaces of lens For simplicity, we will refract it at center (perpendicular to principal axis) –This is called the thin lens model, which does apply to the lenses we talk about
Early Work – Apr. 11 Which lens is a converging lens? Which lens is a diverging lens? Last day for $2 donation to lens fund. Bkwk due Tues. Apr. 17
Conventions Applied to Lenses (P430) f is positive for convex lenses f is negative for concave lenses d o is positive on the object side of the lens d i is positive on the other side (image side) of the lens, where images are real d i is negative on the object side of the lens where images are virtual
Example An object is placed 32.0 cm from a convex lens that has a focal length of 8.0 cm. –Where is the image? –If the object is 3.0 cm high, how high is the image? –Is the image inverted or upright?
Virtual Images When an object is in front of the focal point, a virtual, erect, enlarged image appears A magnifying glass!
Example A convex lens with a focal length of 6.0 cm is held 4.0 cm from an insect that is 0.50 cm long. –Where is the image located? –How large does the insect appear to be?