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NEET PHYSICSWAVEMedium

Question

In a guitar, two strings AA and BB made of same material are slightly out of tune and produce beats of frequency 6 Hz6 \text{ Hz}. When tension in BB is slightly decreased, the beat frequency increases to 7 Hz7 \text{ Hz}. If the frequency of AA is 530 Hz530 \text{ Hz}, the original frequency of BB will be:

A

524 Hz524 \text{ Hz}

B

536 Hz536 \text{ Hz}

C

537 Hz537 \text{ Hz}

D

523 Hz523 \text{ Hz}

Step-by-Step Solution

Given, the frequency of string AA is fA=530 Hzf_A = 530 \text{ Hz}. The beat frequency produced by strings AA and BB is 6 Hz6 \text{ Hz}. Therefore, the original frequency of string BB can be either: fB=fA+6=536 Hzf_B = f_A + 6 = 536 \text{ Hz} or fB=fA6=524 Hzf_B = f_A - 6 = 524 \text{ Hz}

The frequency of a stretched string is directly proportional to the square root of its tension (fTf \propto \sqrt{T}). When the tension in string BB is decreased, its frequency fBf_B decreases.

Now, let's analyze both cases with the new decreased frequency fBf_B': Case 1: If fBf_B was 536 Hz536 \text{ Hz}, a decrease in tension would lower the frequency (e.g., to 535 Hz535 \text{ Hz}). The new beat frequency would be 530535=5 Hz|530 - 535| = 5 \text{ Hz}. Here, the beat frequency decreases, which contradicts the given information. Case 2: If fBf_B was 524 Hz524 \text{ Hz}, a decrease in tension would lower the frequency (e.g., to 523 Hz523 \text{ Hz}). The new beat frequency would be 530523=7 Hz|530 - 523| = 7 \text{ Hz}. Here, the beat frequency increases to 7 Hz7 \text{ Hz}, which exactly matches the given condition.

Therefore, the original frequency of string BB must be 524 Hz524 \text{ Hz}.

Exam Context & Concepts Covered

This question aligns with the NEET PHYSICS syllabus, specifically targeting concepts from WAVE. Mastering this topic is crucial for scoring well in the upcoming medical entrance examinations. Solving conceptually related problems will help you understand the nuances of these concepts and improve your problem-solving speed.

PHYSICSWAVEguitarstringsmaterialslightlyproduce

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