An achromatic convergent doublet of two lense in contact has a power of +5 D . The power of converging lens is +6 D . The ratio of the dispersive power of the convergent and divergent lenses is

Step-by-step solution

- The condition of achromatism is W₁ P₁+W₂ P₂=0 array rlrl & W₁ P₁ & =-W₂ P₂ & & W₁ W₂ & =- P₂ P₁ array Now, P₁+P₂=4 D but, Power of converging lens, P₁=5 D Power of diverging lens aligned P₂ & =4 D -P₁ & =4 D -5 D =- D aligned [From ii] From Eq. (i), we have W₁ W₂ =- P₂ P₁ = -(-D) 5 D = 1 5 W₁ W₂ = 1 5