Three thin prisms are combined as shown in figure.

Three thin prisms are combined as shown in figure. The refractive indices of the crown glass for red, yellow and violet rays are $\mu_{r}, \mu_{y_{\text {and }}} \mu_{v}$ respectively and those for the flint glass are $\mu_{r}^{\prime}, \mu_{y}^{\prime}$ and $\mu_{v}^{\prime}$ respectively. Find the ration $A^{\prime} / A$ for which

(a) there is no net angular dispersion and,

(b) there is no net deviation in the yellow ray.