2020 Phase-2 Ray Optics and Optical InstrumentsMirror formula Medium Question 29 of 89 in Ray Optics and Optical Instruments

An object is placed on the principal axis of a concave mirror at a distance of 1.5 f (f is the focal length). The image will be at,

A 3f
B $-3f$
C 1.5 f
D $-1.5f$

The answer is B.

Solution

Using sign convention, $u=-1.5f$, mirror focal length $f=-f$ (concave). $\dfrac{1}{v}+\dfrac{1}{u}=\dfrac{1}{f}\Rightarrow\dfrac{1}{v}=\dfrac{1}{-f}-\dfrac{1}{-1.5f}=-\dfrac{1}{f}+\dfrac{1}{1.5f}=\dfrac{-1.5+1}{1.5f}=\dfrac{-0.5}{1.5f}=\dfrac{-1}{3f}\Rightarrow v=-3f$.

Concept Mirror formula

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89 questions from this chapter have appeared across 25 exam years.