Time taken by light to cross a glass slab of thickness 4 mm and refractive index 3 is

Options

(a) 4×10⁻¹¹ sec
(b) 2×10⁻¹¹ sec
(c) 16×10⁻¹¹ sec
(d) 8×10⁻¹¹ sec

Correct Answer:

4×10⁻¹¹ sec

Explanation:

t = μx / c = (3 × 4 × 10⁻³) / (3 × 10⁸) = 4 x 10⁻¹¹ sec