[" Two lens of focal length "-20cm" and "],[+10cm" are put in combination.Find the "],[" power of the combination."]

Two lenses of focal length 10 cm and -20 cm are placed in contact .What is the total power of the combination?

Two lenses of focal lengths -20cm and +10cm are put in contact.Find power of the combination

Two lenses of focal lengths -20cm and +10cm are put in contact. Find power of the combination (A) -1D (B) -2D (C) +5D (D) +2D

Two thin lenses of focal lengths 20cm and 25cm are placed in contact. The effective power of the combination is

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.

A concave lens of focal length 12 cm and a convex lens of focal length 20 cm are kept in contact with each other . Find the focal length of the combination .

If a convex lens of focal length 20 cm and a concave lens of focal length 30 cm are kept in contract with each other. What will the power of the combination ?

A concave lens of focal length 12 cm and a convex lens of focal length 20 cm are kept in contact with wach other. (i) Find the focal length of the combination. (ii) What will be the behaviour fo the combination ?

Find the effective power and focal length of two lenses of focal lengths 50 cm and -200 cm when put in contact. What is the nature of the combined lens?