八年级物理笔记上中.docx

7.02 Concave and Convex MirrorConcave mirror:- Definition: a mirror with a surface that curves inward (the edges curve toward the observer)- Objects distance is large/ object at infinity: incident rays nearly parallel.l Sunlight g focal point - Concave mirror converge light rays Whats inside a concave mirror?- C: geometric center- r: radius of curvature- M: center of the mirror- Principle Axis: the straight line perpendicular to the surface of the mirror, divides the mirror in half- F: focal point: the point at which light rays parallel to the principal axis meet after being reflected by a mirror (/ g F) (F 0)- : focal length: the distance between the focal point and the mirror - Principal plane- Path reversed: F g /Image formed: intersection of reflected rays- Rays for image finding 1. / g F2. F g /3. C g M- Real image: an image formed by the converging of light rays (seen on a screen) di0Image and positiondiTypeSizehi Sidedo = infinity di = fRealPointhi = 0Same do 2FF di 2FRealDiminished Inverted Same do = 2F di = 2FRealSame Inverted Same F do 2FRealEnlargedInverted Same do = Fdi = infinity Real Never meets do FVirtual Enlarged Erected Opposite Application- Use: car headlight; producing magnified images, reflecting telescope Convex mirror- Definition: a mirror with a surface that curves outward a reflective surface with edges that curve away from the observer - F: focal point: the point at which light rays parallel to the principal axis meet after being reflected by a mirror (F g /) (F 0)- Convex mirror diverges light rays Image formed: intersection of reflected rays- Rays for image finding 1. / g F2. F g /3. C g M- Image formed: virtual image, smaller image, right side up, di 0|di| = do (negative)Same VirtualConcavePositive do rr di Reduced, InvertedReal r do di Enlarged, Inverted Real do 0 |di| do (negative)Enlarged Virtual ConvexNegative do 0 | |di| 0 (negative)Reduced Virtual Mirror Equation 1. 1/ = 1/do + 1/dil = focal lengthl do = distance of objectl di = distance of image 2. m = hi/ho = -di/dol m = magnification factor |m| 1, reduced image m 0, inverted image l hi = height of imagel ho = height of object Sign conventions when using the mirror formula:a) All distances are measured from the principle plane (vertex) of a curved mirrorb) Distance of object (do) and of real images g (di) = positive (+)c) Distances of virtual images g (di) = negative (-)d) Object (ho) and of image heights (hi) l Upright: positive (+)l Inverted: negative (-)e) Concave mirror focal length (): positive (+)f) Convex focal length (): negative (-)Magnification- |m| 1 = reduced image- m g slow down more = bent toward normal l n V violet N red n2), at a certain angle of incident, the refracted ray lines along the boundary. This angle of incidence is the critical angle (c)- Critical angle of water: 49, v slow, n 1.33- Critical angle of glass: 41 , v slower, n = 1.42- n water n glassApplication- Rear reflector- Optical fibers: very thin, flexible rod made of special glass or transparent plastics - Whatever angle the light beam hits the corner it will reflect back along its original pathPeriscopeBinoculars7.13 Refraction calculationn1 sin 1 = n2 sin 2- n1 & n2 = reflex index of different object- 1 & 2 = angle of incident and angle of refraction l If 1 = 0 then 2 = 0l If 1 increase then 2 increase l n1 n2 = bends away from normal Index of refraction (n): (vacuum to material