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9.An object is 4cm high. It is desired to form a real image 2cm high at 60cm from the mirror. What type of mirroris needed and what should be its focal length?{Ans: - 40 cm) |
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Answer» Height of object ho = 4 cm Focal lenght of convex mirror = ? cm Object distance u = ? cm Image distance v = 60 cm Image height hi = 2 cm Magnification m = hi/ho = 2/4=1/2 v/u = 1/2 60cm/u = 1/2 u = 120 cm mirror formula: 1/v + 1/u = 1/-f 1/-f = 1/v + 1/u = 1/60 + 1/120 = 3/120 = 1/40 ⇒ f= -40 cm |
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