Question

two lenses of power 6d and -1.5d.find the focal length and mention the nature of each lens

Answer 1

in the first situation the nature is real and virtual.

in the second situation the nature is virtual and erect.

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Answer 2

CASE 1:

Here P=+D Since power is positive , so the lens is convex lens

Focal length, f = 1/P=1/2=0.5m=50cm

CASE 2:

Now,P=-4 Since power is negative ,so lens is concave.

Focal length,f=1/P=1/-4=-0.25m=-25cm