(i) Calculation of speed of light
(ii) Calculation of angle of incidence at face AB
(i) µ=‌

sin‌( A+δm 2 )

sin‌(‌ A 2 )

‌=‌

sin‌( 60∘+30∘ 2 )

sin‌(‌ 60∘ 2 )

=√2
‌ Also ‌‌‌µ‌=‌

c

v

⇒v=‌

3×108

√2

m∕ s
v‌=2.122×108m∕ s
(ii)
At face AC, let the angle of incidence be r2.
For grazing ray, e=90∘
⇒‌‌µ=‌

1

sin‌r2

⇒r2=sin‌−1(‌

1

√2

)=45∘
Let angle of refraction at face AB be r1.
Now r1+r2=A
∴‌‌r1=A−r2=60∘−45∘=15∘
Let angle of incidence at this face be i
‌µ‌=‌

sin‌i

sin‌r1

⇒‌‌µ‌=√2=‌

sin‌i

sin‌15∘

∴‌i‌=sin‌−1(√2⋅sin‌15∘)