Question

A ray of light incident at an angle θ on a refracting face of a prism emerges from the other face normally. If the angle of the prism is 5° and the prism is made of a material of refractive index 1.5, the angle of incidence is ______.

विकल्प

• 7.5°

• 5°

• 15°

• 2.5°

Answer 1

A ray of light incident at an angle θ on a refracting face of a prism emerges from the other face normally. If the angle of the prism is 5° and the prism is made of a material of refractive index 1.5, the angle of incidence is 7.5°.

Explanation:

In thin prisms, the distance between the refracting surfaces is ineligible and the angle of prism (A) is very small. Since A = r₁ + r₂, therefore if A is small then both r₁ and r₂ are also small, and the same is true for i₁ and i₂.

A = 5°

μ = 1.5

i₂ = 0°

r₂ = 0°

r₁ + r₂ = A

r₁ = A - r₂ = 5 – 0 = 5°

μ = `(sini1)/(sinrlμ) = (sinil)/(sinrl)`

⇒ `sini1 = μsinr1`

= `1.5 xx sin 5°`

= 1.5 xx 0.087`

= 0.1305

= 7.5°