Question

A diverging lens, focal length f₁ = 20 cm is separated by 5 cm from a converging mirror, focal length f₂ = 10 cm. Where should an object be placed from the lens so that a real image is formed at the object itself ?

• A. 30 cm
• B. 60 cm
• C. 10 cm
• D. 40 cm

Answer 1

Answer: (B)

60 cm

Answer 2

For lens f = –20, u = ?, v = – (20 – 5) = – 15

$\frac { 1 } { - 20 }$ = $\frac { 1 } { - 15 }$–

= $\frac { 1 } { 20 } - \frac { 1 } { 15 }$

u = – 60