Two prism made of material of same refractive index and having angles of the prism 65° and 60° respectively are combined to form a glass block as shown. If for any ray passing across the block the minimum angle of deviation in 3° then refractive index for the material of the prism is

1.6

The correct answer is option (2) : 1.6

According to the given question angle of minimum deviation is 3°

$⇒(\mu - 1)A_1-(\mu - 1) A_2=3$

$⇒(\mu -1) 65- (\mu -1) 60=3$

$⇒65\mu - 65 - 60 \mu + 60 = 3$

$⇒5\mu - 5= 3$

$⇒ 5\mu = 8 $

$⇒\mu = 1.6$