The dispersive powers of the materials of two lenses forming an achromatic combination are in the ratio of `4:3`. Effective focal length of the two lenses is + 60 cm then the focal lengths of the lenses should be

The dispersive powers of glasses of lenses used in an achromatic pair are in the ratio 5 : 3. If the focal length of the concave lens is 15 cm , then the nature and focal length of the other lens would be

The dispersive powers of glasses of lenses used in an achromatic pair are in the ratio 5 : 3. If the focal length of the concave lens is 15 cm , then the nature and focal length of the other lens would be

The dispersive powers of glasses of lenses used in an achromatic pair are in the ratio 5 : 3. If the focal length of the concave lens is 15 cm , then the nature and focal length of the other lens would be

The dispersive powers of the materials of the two lenses are in the ratio 4:3 .If the combination of these two lenses is of focal length 60 cm,then the focal lengths of the component lenses are:

Dispersive powers of materials used in lenses of an achromatic doublet are in the ratio 5:3 .If the focal length of concave lensis 15 cm,then the focal length of the other lens will be- (1)=-9cm (2)+9cm (3)-12cm,(4)+12cm

The dispersive powers of crown and flint glasses are 0.02 and 0.04 respectively. In an achromatic combination of lenses the focal length of flint glass lens is 40 cm . The focal length of crown glass lens will be

To obtain an achromatic combination using the lenses of same material the two lenses should be :

Two lenses are placed in contact with each other and the focal length of combination is 80 cm . If the focal length of one is 20 cm , then the power of the other will be