Question

Power of the lens is -40 its focal length is a.4 m b. -40 m c. 40 cm d.5 cm

Answer 1

1/-40D is the power of the lens bcz..

p=1/f

Answer 2

Power = 1/ f (in metres)

So - 40 = 1/f

i.e f =-1/40 metres or 2.5 cm