Two identical prism of index `sqrt3` are kept as shown in the figure. A light ray strikes the first prism at face AB. Find,
(a) the angle of incidence, so that the emergent ray from the first prism has minimum deviation.
(b) through what angle the prism DCE should be rotated about C so that the final emergent ray also has minimum deviation. `

Answer

(A)`I=60^(@),(B)60^(@)`(anticlockwise)

Explanation

(a) `2r_(1)=60^(@)rArrr_(1)=60^(@) rArr sqrt(3)=("sin" i_(1))/("sin" 30^(@)) rArr "sin" i_(1)=sqrt(3//2)rArr i_(1)=60^(@)`
(b) Angle of incidence at face `DC`should be `60^(@)`for minimum deviation .So prism should be rotated `60^(@)`ACW.