Question

A source of unknown frequency gives 4 beats/s when sounded with a source of known frequency 250 Hz. The second harmonic of the source of unknown frequency gives five beats per second, when sounded with a source of frequency 513 Hz. The unknown frequency is

(a) 240 Hz

(b) 260 Hz

(c) 254 Hz

(d) 246 Hz

Answer 1

Correct option (c) 254 Hz

Explanation:

Let v be frequency of the unknown source. As it gives 4 beats per second when sounded with a

source of frequency 250 Hz,

Second harmonic of this unknown source = 492 Hz or 508 Hz which gives 5 beats per second. when sounded with a source of frequency 5 13 Hz.

Therefore unknown frequency, v - 254 Hz.