Question

A tuning fork of frequency 100 when sounded together with another tuning fork of unknown frequency produces 2 beats per second. On loading the tuning fork whose frequency is not known and sounded together with a tuning fork of frequency 100 produces one beat, then the frequency of the other tuning fork is

• A. 102
• B. 98
• C. 99
• D. 101

Answer 1

Answer: (A)

102

Answer 2

Suppose n_A = known frequency = 100 Hz, n_B = ?

x = 2 = Beat frequency, which is decreasing after loading (i.e. x↓) 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 = 100 + 2 = 102 Hz.