An isosceles trapezium of reflecting material of refractive index `sqrt 2` and dimension of sides being 5cm, 5cm, 10cm and 5 cm. The angle of minimum deviation by this when light is incident from air and emerges in air is:

Options

A. `22 1/2 .^(@)`
B. `45^(@)`
C. `30^(@)`
D. `60^(@)`

Answer

C

Explanation

If we complete the trapezium as shown it becomes an equilibrium triangle
`rArr A=60^(@)`
`(sin[(A+delta_("min"))/2])/(sin A/2) =mu`
`(sin[(60+delta_("min"))/2])/(sin(60/2)) =sqrt(2)`
`delta_("min") =30^(@)`