[UPSC CSE 2023] Geometrical Optics (Q124, 15M)

Obtain condition for achromatism of two thin lenses separated by a finite distance. If the dispersive powers of the materials of the two lenses are 0\cdot020 and 0\cdot028, their focal lengths are 10\text{ cm} and 5\text{ cm}, respectively. Calculate the separation between them in order to form achromatic combination.