A simple microscope consists of a concave lens of power −10 D and a convex lens of power +20 D in contact. If the image formed at infinity, then the magnifying power (D=25 cm) is:

A compound lens is made of a convex lens of power 10 D and a concave lens of power 5 D. An object 2 cm high is placed in front of this combination at a distance 40 cm from it. Find nature and size of the image formed.

A compound lens is made of a convex lens of power 10 D and a concave lens of power 5 D. An object 2 cm high is placed in front of this combination at a distance 40 cm from it. Find nature and size of the image formed.

A convex lens of focal lenth 30 cm and a concave lens of focal length 60 cm are placed in contact.Find the power of the combination.

If a convex lens of focal length 80 cm and a concave lens of focal length 50 cm re combined together ,what will be their resulting power?

Under what conditions will a convex lens have a negative and a concave lens a positive power?

If two lenses of power +1.5 D and +1.0 D are placed in contact ,then the effective power of combination will be

Two lenses of powers 10D - 5D are placed in contact Calculate the power of the new lens.