Question Detail
Question
The diagram shows a ray of monochromatic light passing through a semi-circular glass block. What is the refractive index of the glass?
Correct Answer
Option C is the correct answer.
Detailed Explanation
From the diagram (as seen in similar questions like on page 36, Q2), the ray enters the curved surface perpendicularly, so it goes undeviated into the glass. It then strikes the flat surface of the glass block. The ray inside the glass makes an angle of incidence of 50° with the normal to the flat surface. The ray emerges into the air parallel to the flat surface, meaning the angle of refraction in air is 90°. This implies that 50° is the critical angle for the glass-air interface.Using Snell's Law for the critical angle: nglass * sin(θcritical) = nair * sin(90°).Given nair = 1, and θcritical = 50°.nglass * sin(50°) = 1 * 1nglass = 1 / sin(50°)nglass = 1 / 0.7660nglass ≈ 1.305 ≈ 1.31.
Hint
Recall Snell's Law and the definition of critical angle. The ray emerging parallel to the surface means the angle of refraction in air is 90 degrees.