Question

bifocal lense of power is 2D and _4D . find the range of vision

Answer 1

power of the lens = 2D + (-4D) = -2D.

also, power = 100/f(cm) = 100/2 = 50 cm

so, range is 50 cm.

Answer 2

P=1/f
f =1/p
=1/2
=0.5
0.5×100
50