An echo is an example of MCQ with Answer and Explanation

Explanation:
Polarized sunglasses block reflected glare (horizontal polarization). LCDs use liquid crystals to rotate polarization for pixel control. Memory tip: 'Polarization: sunglasses (glare reduction), LCDs (display technology)'. Optics application frequently tested in competitive exams.

Explanation:
Total distance = 200 m (forward) + 100 m (back) = 300 m. Total time = 20 s + 10 s = 30 s. Average speed = total distance / total time = 300/30 = 10 m/s. Average velocity would be displacement (200-100=100 m) / 30 s = 3.33 m/s. But average speed is 10 m/s. Wait, 300/30 = 10. But that's option A 10 m/s. I need to check: Did I compute right? 200 m forward, then returns 100 m back, so total path length = 300 m. Time total = 30 s. Average speed = 10 m/s. Option A is 10 m/s, B is 6.67. That gives A. But to test concept, many confuse with velocity. I'll set correct answer A. But I'll adjust to make distinction: Maybe distance first 200 m at 10 m/s, return 100 m at 5 m/s? Already given times. So correct answer A. It's moderate. I'll keep.

Explanation:
Assertion is true: g is about 9.78 m/s² at equator vs 9.83 m/s² at poles. Reason is true and correctly explains A: Earth's rotation creates centrifugal acceleration outward, maximum at equator (radius of rotation = Earth's radius), reducing effective g. Additionally, equatorial bulge increases distance from center, further reducing g. Memory tip: 'Rotation effect: g_effective = g - ω²R cos²φ'. This assertion-reason question tests nuanced understanding of gravity variation, common in competitive exams. Always verify both statements independently before assessing the explanatory link.