The refractive index of water is 4/3. The speed of light in water is:
A. 2.25×10⁸ m/s
B. 1.5×10⁸ m/s
C. 3×10⁸ m/s
D. 4×10⁸ m/s
Answer: Option A
Solution (By JKSSB Mock Tests)
Refractive index n = c/v, where c = 3×10⁸ m/s (speed in vacuum). Thus v = c/n = (3×10⁸)/(4/3) = 3×10⁸ × 3/4 = 9/4 × 10⁸ = 2.25×10⁸ m/s. This direct formula application is fundamental in optics. Memory aid: 'Higher n ⇒ slower light in medium'. Competitive exams frequently test this calculation with common refractive indices (water 4/3, glass ~1.5). Always use c = 3×10⁸ m/s unless specified otherwise, and ensure unit consistency (m/s here).
Explanation:
LEDs are highly efficient, converting ~80-90% of electrical energy into light, rest heat. Incandescent bulbs ~10% efficient. LED long life, low power. Blue LED Nobel prize 2014.
No comments yet. Be the first to start the discussion!