A tuning fork A produces 5 beats/second with tuning fork B of frequency 256 Hz. If a little wax is applied to fork A, the beat frequency becomes 2 beats/second. The original frequency of fork A was: MCQ with Answer and Explanation

A tuning fork A produces 5 beats/second with tuning fork B of frequency 256 Hz. If a little wax is applied to fork A, the beat frequency becomes 2 beats/second. The original frequency of fork A was:
A. 261 Hz
B. 251 Hz
C. 258 Hz
D. 254 Hz
Answer: Option A
Solution (By JKExamLibrary)
The beat frequency is |fA - fB|. So fA is either 256+5=261 Hz or 256-5=251 Hz. Adding wax increases mass, which strictly decreases frequency. If fA was 261, decreasing it brings it closer to 256, reducing beats to 2 (e.g., 258-256=2). If it was 251, decreasing it would increase the beats (e.g., |248-256|=8). Thus, it was 261 Hz.

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