Two identical thin biconvex lenses of focal length 15 cm and refractive index 1.5 are in contact with each other. The space between the lenses is filled with a liquid of refractive index 1.25. The focal length of the combination is ______ cm.

Two identical equiconvex lenses of refractive index 3//2 and focal length 16 cm are kept in contact. The space between the lenses is filled with water of refractive index 4//3 . What is the focal length of the combination ?

Two equi convex lenses each of focal lengths 20 cm and refractive index 1.5 are placed in & contact and space between them is filled with water of refractive index 4/3 . The combination works as

Two concave lenses L_1 and L_2 are kept in contact with each other. If the space between the two lenses is filled with a material of smaller refractive index, the magnitude of the focal length of the combination

Two thin converging lenses of focal length 15 cm and 30 cm are held in contact with each other. The focal length of the combination is

Two plano concave lenses of glass of refractive index 1.5 have radii of currature 20cm and 30cm respectively. They are placed in contact with the curved surface to wards each other and the space between them is filled with a liquid of refractive index 3. The focal length of the combination is (in cm) (A) 12 (B) 16 (C) -92

Two plano concave lenses of glass of refractive index 1.5 have radii of currature 20cm and 30cm respectively.They are placed in contact with the curved surface to wards each other and the space between them is filled with a liquid of refractive index (5)/(2) . The focal length of the combination is (in cm)

Two convex lenses of focal lengths 25 cm and 15 cm are placed in contact with each other. Find the focal length of combination.