Question

The focal length of a concave lens with power -2 D is ______.

a) 50 cm b) - 20 cm c) 20 cm d) -50 cm​

Answer 1

Power = -2 D

F = 1/Power

F = -1/2 * 100

F = -50 cm

Answer 2

$\huge\boxed{\underline{\bf { \red S \green O \pink L \blue U \orange T \purple I \red O \pink N \green{..}}}}$

$\: \: \: \: \bullet \: \sf Power = -2$

$\bigstar \: \boxed{ \sf Forcal \: length = \frac{1}{Power}}$

$\mapsto \sf f = \frac{1}{ - 2} × 100$

$\mapsto \sf f = - 50 \: cm$