wave_mechanics mock_test_waves_and_acoustics Question 15
Question: A tuning fork of known frequency 256 Hz makes 5 beats per second with the vibrating string of a piano. The beat frequency decreases to 2 beats per second when the tension in the piano string is slightly increased. The frequency of the piano string before increasing the tension was
Options:
A) 256 + 5 Hz
B) 256 + 2 Hz
C) 256 - 2 Hz
D) 256 - 5 Hz
Show Answer
Answer:
Correct Answer: D
Solution:
[d] Suppose $ n _{p} $ = frequency of piano =? $ (n _{p}\propto \sqrt{T}) $
$ n _{f} $ = Frequency of tuning fork = 256 Hz x = Beat frequency = 5 bps, which is decreasing $ (5\to 2) $ after changing the tension of piano Wire Also, tension of piano wire is increasing so $ n _{p}\downarrow $ Hence $ n _{p}\uparrow -n _{f}=x\downarrow \to $ Wrong $ n _{f}-n _{p}\uparrow =x\downarrow \to $ Correct $ \Rightarrow n _{p}=n _{f}-x=256-5Hz.
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BETA
