The focal length of a combination of two lenses is doubled if the separation between them is doubled. If the separation is increased to 4 times, the magnitude of focal length is

Focal length of combination of two thin lenses is 1 m. Calculate the power of one lens if the focal length of other lens is 30 cm.

The focal length of the combination of two thin lenses in contact is 80 cm. If the focal length of one lens is -20 cm, what is the power of the other lens ?

If the lens is double concave then its focal length is

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 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 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