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A source of unknown frequency gives 4 beats/s, when sounded with a source harmonic

A source of unknown frequency gives 4 beats/s, when sounded with a source harmonic of the source of unknown frequency gives 5 beats/s, when sounded with a source of frequency 513 Hz. The unknown frequency is

Options

(a) 246 Hz
(b) 240 Hz
(c) 260 Hz
(d) 254 Hz

Correct Answer:

254 Hz

Explanation:

When sounded with a source of known frequency fundamental frequency = 250 +- 4 Hz. = 254 Hz or 246 Hz. second harmonic if unknown frequency (suppose) 254 Hz = 2 x 254 = 508 Hz. As it is gives 5 beats 508 + 5 = 513 Hz.
Hence, unknown frequency is 254 Hz.

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