Question

If a small object of length l is at 20cm in front of convex mirror of focal length 20cm. If the object is placed along the principal axis of mirror then length of image formed is –

• A. l
• B. l / 2
• C. l / 4
• D. None of these

Answer 1

Answer: (C)

l / 4

Answer 2

u = –20 cm, f = +20 cm ; m =

m = $\frac { + 20 } { + 20 - ( - 20 ) }$ = $\frac { 1 } { 2 }$

M = –m² = $- \frac { 1 } { 4 }$ = $\frac { \text { length of image } } { \text { length of object } }$

\ length of image = $- \frac { 1 } { 4 }$(length of object) = $- \frac { 1 } { 4 } \ell$