Reflection of waves
Reflection of waves is a Science & Technology concept from the MPSC syllabus, tested in 2 past MPSC questions (2020, 2021). Below are those real questions with their correct answers and explanations, plus the concepts worth being comfortable with first.
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Real questions that test this
जेव्हा एखाद्या ध्वनी तरंगाचे संपीड़न दृढ भंतीवर आदळेल तेव्हा त्याचे प्रतिबिंबित रूप हे : When a compression of sound waves is incident on rigid wall, it is reflected as :
At a rigid boundary, particle displacement has a node and pressure has an antinode -- the opposite of what happens at a free/open boundary. This means a pressure compression reflects back as a compression (not a rarefaction), with no phase change in the pressure wave. (The displacement wave does invert by 180 degrees, but the question is about the compression/pressure wave itself.)
लेसर किरण पृथ्वीवरून चंद्रकड सोडूननंतर चंद्राच्या पृष्ठभागापासून परावर्तित होऊन पृथ्वीवर परत येण्यास 2.56 सेकंद लागतात. तर चंद्राच्या पृथ्वीभोवतीच्या परिभ्रमण कक्षेची त्रिज्या किती ? A laser light beamed at the Moon takes 2.56 s to return to earth after reflection at the Moon's surface. How much is the radius of the lunar orbit around the Earth ?
Time taken for round trip is 2.56 s, so time to reach the moon (t) = 2.56 / 2 = 1.28 s. Distance (Radius) = Speed of light * time = (3 × 10⁸) × 1.28 = 3.84 × 10⁸ m.