While solving a problem with a convex mirror of focal length

PHYSICS · Single correct · CBSE · Physics · Light — Reflection and Refraction · Light — Reflection and Refraction

Problem

15\,\text{cm}

, a student substituted

f=-15\,\text{cm}

and

u=-20\,\text{cm}

in the mirror formula

\dfrac{1}{f}=\dfrac{1}{v}+\dfrac{1}{u}

. Which statement correctly points out the sign error? (a)

u

must be

+20\,\text{cm}

;

f

is correctly negative (b)

f

must be

+15\,\text{cm}

;

u

is correctly negative (c) Both

f

and

u

should be negative because they are measured along the incident ray (d) Both

f

and

u

should be positive