Question

find the focal length (in cm) of a lens of power -2D.Identify the type of this lens.
​

Answer 1

$f = 1 \div p \\ f = 1 \div - 2 = - 0.5m$

so it is concave lense.

I THINK IT IS HELPFUL TO YOU.....

Answer 2

Power of lens= -2D

Now we know that

Power=1/focal length (in meters)

So, -2=1/f

So, f=1/-2

So, f= -0.5m

Therefore,

Focal length is - 0.5 , i.e, -50cm.

As the focal length and power is negative it is Concave lens.

Hope it helps you