Physics Help Forum Spherical Concave Mirror

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 Dec 7th 2010, 03:19 AM #1 Junior Member   Join Date: Dec 2010 Posts: 1 Spherical Concave Mirror A spherical concave mirror (not parabolic) has a radius of 4 cm on which a ray is incident 3 cm from the principle axis, as shown in the figure. Since the mirror is not parabolic the ray doesn’t pass through the focus. After reflection on A and then on B, the ray crosses the principal axis at point P. Find the distance of P from C. *The answer should be according to the following convention: If the ray passes the principle axis left of C the distance is positive, else negative.
 Feb 13th 2011, 09:42 AM #2 Senior Member   Join Date: Dec 2008 Location: Udupi, Karnataka, India Posts: 292 Draw CD perpendicular to the parallel ray. Join CA and CB. Let ACF line intersects AB at E. Now CD = 3 cm and CD = 4 cm. Let $\displaystyle \angleDAC$ be θ. So sinθ = 3/4. Now angle DAC = CAF = CBF = CBP = θ. Angle CFB = 2θ. And angle PCB = 3θ.Then angle CPB = 180 - 4θ. Now use sine rule. PC/sinθ = CB/sin(180 - 4θ.) CB = 4 cm. Find PC.

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