Question

Two prisms A and B have dispersive powers of 0.012 and 0.018 respectively. The two prisms are incontact with each other. The prism A produces a mean deviation of ${1.2}^{\circ }$, what is the mean deviation produced by B if the combination is achromatic?

• A. ${3.6}^{\circ }$
• B. ${0.8}^{\circ }$
• C. ${0.4}^{\circ }$
• D. ${1.8}^{\circ }$

Answer 1

The correct option is B ${0.8}^{\circ }$

$w_1{D}_1=w_2{D}_{2}0.012\times 1.2=0.018D_2{D}_2=\frac{12\times 12}{18}=\frac{2\times 1.2}{3}D={0.8}^{\circ }$