In a nuclear reactor, the function of a moderator is to MCQ with Answer and Explanation
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Question #1
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The refractive index of water is 4/3. The speed of light in water is:
Correct Answer: Option D
Explanation:
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).
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).
Question #2
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Soft iron is universally preferred for making the core of a transformer or an electromagnet because it possesses:
Correct Answer: Option A
Explanation:
A transformer core is subject to alternating magnetic fields, tracing out a hysteresis loop repeatedly. To minimize energy loss (hysteresis loss), the area of this loop must be small, requiring low coercivity (easily demagnetized). It also requires low retentivity so it loses magnetism rapidly when current stops. Steel, conversely, has high retentivity and coercivity, used for permanent magnets.
A transformer core is subject to alternating magnetic fields, tracing out a hysteresis loop repeatedly. To minimize energy loss (hysteresis loss), the area of this loop must be small, requiring low coercivity (easily demagnetized). It also requires low retentivity so it loses magnetism rapidly when current stops. Steel, conversely, has high retentivity and coercivity, used for permanent magnets.
Question #3
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A car moving with speed 54 km/h is stopped in 5 s. The distance covered before stop is
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