Crown and flint glass lenses are joined to form an achromatic lens. Making use of the lensmaker formula for thin lenses, a)Show that the focal lengths for this optical device satisfy the equation, ñ is the value of the index of refraction of the glass in the center of the visible spectrum and ∆λ is the wavelength spread (∼ 3000Å) in the visible spectrum. (b) For crown glass αc = 0.0169 and for flint glass αf = 0.0384. Show that one should wear a Crown convergent lens together with a divergent flint to obtain an achromatic convergent lens.

2. Crown and flint glass lenses are joined to form an achromatic lens. Making use of the lensmaker formula for thin lenses, 1 } = (-1) (1 2 +22) (n (7 -122). R (a) Show that the focal lengths for this optical device satisfy the equation, ac af ff + = 0 fe a = 1/(n-1)dn AX, is the value of the index of refraction of the glass in the center of the visible spectrum and delta lambda is the wavelength spread (-3000A) in the visible spectrum. (b) For crown glass ac = 0.0169 and for flint glass af = 0.0384. Show that one should wear a Crown convergent lens together with a divergent flint to obtain an achromatic convergent lens.