Physics 2C lecture 18-20 PDF

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Physics 2C Lecture 18 & 19 & 20 Mirror and Lenses 1. Mirror a. Reflects i. Reflect light by exact same angle as incident angle ii. Angle incident = Angle Reflected b. Reflection in a plane mirror i. 2 key features 1. Reflected picture appears behind mirror 2. Left and right images are flipped c. Parabolic Mirror i. May be approximated by sphere for small angles d. Spherical Mirror i. Object behind c 1. Reduced inverted image between c and f ii. Object between c and f 1. Enlarged inverted image behind c iii. Object in front of f 1. Enlarged image behind mirror e. Convex spherical mirror i. Image appears… 1. Reduced size or shrunk 2. Same side as object or behind mirror 3. Not inverted or right side up f. Mirror equation i. (1/l) + (1/l’) = (1/f) 1. l = distance from object to mirror 2. l’ = distance from image to mirror ii. f = 2r 1. f = focal length 2. r = radius of mirror curve iii. m = h / h’ = l / l’ 1. m = magnification 2. h = height of object 3. h’ = height of image

g. sign conventions i. positive l or l’ if… 1. same side as object from the mirror ii. negative l or l’ if… 1. opposite side as object from error iii. positive h if… 1. image is right side up iv. negative h if 1. image is inverted

2. Lens a. Refracts i. Bends light by angle explained by Snell’s Law ii. Snell’s Law 1. (n1) ( sin theta 1) = (n2) (sine theta 2) b. 2 Types i. Convex lens converges ii. Concave lens diverges c. Variables i. f is focal length ii. l is distance between lens and object iii. l’ is distance between lens and image d. Lens equation i. (1/l) + (1/l’) = (1/f) ii. (1/f) = (n-1) ((1/R1) – (1/R2)) 3. Ray Tracing a. Ray 1 parallels to x axis and pass through focal point b. Ray 2 pass directly across midline c. Ray 3 passes through focal point and extends parallel to x axis 4. Virtual Images for Lens a. Image is… i. right side up ii. On the same side of mirror as the object 5. Human Perception of Size a. We judge size by proportion of the total viewing angle that is filled by the object b. To magnify an object = move it closer to our eyes i. But our focusing is limited to minimal distance 25cm

c. Short sightedness i. Means you can’t see things from far away ii. Occurs when focal point is in front of retina d. Far sightedness i. Means you can’t see things close up ii. Occurs when focal point is behind retina 6. 2 Lens System a. 2 Lens i. One objective lens ii. One eyepiece lens b. Examples i. Microscope 1. Magnifies things close up 2. Small objective lens focal length ii. Telescope 1. Magnifies things far from objective 2. Large objective focal length...