Q

A ray of light enters a rectangular glass slab from air at an angle of 40 degrees to the normal. If the refractive index of glass with respect to air is 1.5 and the velocity of light in air is 3 x 10 m/s, what is the velocity of light inside the glass slab?

RRB Group D 04 Aug, 2026 (4:30 PM - 6:00 PM) 2026
✓ Answer: B 2 x 10 m/s
Refractive index n = c/v. Thus v = 3×10⁸/1.5 = 2×10⁸ m/s.
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