Q127 / 150 · MHT CET 2026 (17 April Shift 1) · Physics
A and B are two wires whose fundamental frequencies are 256 Hz and 382 Hz respectively. When third harmonic of A and the second harmonic of B are sounded together, the number of beats heard in two second will be
- Correct answerA$8$
- B$6$
- C$4$
- D$2$
Solution
Fundamental frequency of wire A, $f_A = 256$ Hz
Fundamental frequency of wire B, $f_B = 382$ Hz
Frequency of the third harmonic of A, $f_1 = 3 f_A = 3 \times 256 = 768$ Hz
Frequency of the second harmonic of B, $f_2 = 2 f_B = 2 \times 382 = 764$ Hz
Beat frequency, $n = |f_1 - f_2| = |768 - 764| = 4$ Hz
Number of beats heard in one second is $4$.
Number of beats heard in two seconds is $4 \times 2 = 8$.
Fundamental frequency of wire B, $f_B = 382$ Hz
Frequency of the third harmonic of A, $f_1 = 3 f_A = 3 \times 256 = 768$ Hz
Frequency of the second harmonic of B, $f_2 = 2 f_B = 2 \times 382 = 764$ Hz
Beat frequency, $n = |f_1 - f_2| = |768 - 764| = 4$ Hz
Number of beats heard in one second is $4$.
Number of beats heard in two seconds is $4 \times 2 = 8$.
Hence, the correct answer is option: 'A'.