An achromatic combination of lenses is formed by joining

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 40cm. The focal length of crown glass lens will be

Two thin lenses, one of crown glass and the other of flint glass are put in contact to give an achromatic system of focal length 50 cm. Find the focal length of the two lenses separately.

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An achromatic convergent system of focal length +20cm is made of two lenses (in contact) of materials having dispersive powers in the ratio 1:2. Their focal lengths must be respectively.