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NEET PHYSICSWAVEMedium

Question

A tuning fork of frequency 512 Hz512 \text{ Hz} makes 4 beats/s4 \text{ beats/s} with the vibrating strings of a piano. The beat frequency decreases to 2 beats/s2 \text{ beats/s} when the tension in the piano strings is slightly increased. The frequency of the piano string before increasing the tension was:

A

510 Hz510 \text{ Hz}

B

514 Hz514 \text{ Hz}

C

516 Hz516 \text{ Hz}

D

508 Hz508 \text{ Hz}

Step-by-Step Solution

  1. Determine possible initial frequencies: The frequency of the tuning fork is f=512 Hzf = 512 \text{ Hz}. The beat frequency is 4 beats/s4 \text{ beats/s}. Therefore, the initial frequency of the piano string (fpf_p) can be either 512+4=516 Hz512 + 4 = 516 \text{ Hz} or 5124=508 Hz512 - 4 = 508 \text{ Hz} .
  2. Analyze the effect of tension: When the tension in a string increases, its fundamental frequency increases because frequency is directly proportional to the square root of tension (fTf \propto \sqrt{T}) .
  3. Determine the correct frequency:
  • If the initial frequency was 516 Hz516 \text{ Hz}, increasing the tension would increase the frequency further (e.g., to 518 Hz518 \text{ Hz}). The new beat frequency with the 512 Hz512 \text{ Hz} tuning fork would be 518512=6 beats/s|518 - 512| = 6 \text{ beats/s}, which represents an increase in the beat frequency.
  • If the initial frequency was 508 Hz508 \text{ Hz}, increasing the tension would increase the frequency closer to 512 Hz512 \text{ Hz} (e.g., to 510 Hz510 \text{ Hz}). The new beat frequency would be 510512=2 beats/s|510 - 512| = 2 \text{ beats/s}, which is a decrease and matches the condition given in the problem. Therefore, the original frequency of the piano string was 508 Hz508 \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.

PHYSICSWAVEtuningfrequencybeatssvibratingstrings

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