Question

When a tuning fork of frequency 341 is sounded with another tuning fork, six beats per second are heard. When the second tuning fork is loaded with wax and sounded with the first tuning fork, the number of beats is two per second. The natural frequency of the second tuning fork is

• A. 334
• B. 339
• C. 343
• D. 347

Answer 1

Answer: (D)

347

Answer 2

n_A = Known frequency = 341 Hz, n_B = ?

x = 6 bps, which is decreasing (i.e. x↓) after loading (from 6 to 1 bps)

Unknown tuning fork is loaded so n_B↓

Hence n_A – n_B↓ = x↓ ... (i) $\longrightarrow$ Wrong

n_B↓ – n_A = x↓ ... (ii) $\longrightarrow$ Correct

⇒ n_B = n_A + x = 341 + 6 = 347 Hz.