Wave Mechanics Beats Question 11
Question: A tuning fork gives 5 beats with another tuning fork of frequency 100 Hz. When the first tuning fork is loaded with wax, then the number of beats remains unchanged, then what will be the frequency of the first tuning fork
[MP PMT 1985]
Options:
A) 95 Hz
B) 100 Hz
C) 105 Hz
D) 110 Hz
Show Answer
Answer:
Correct Answer: C
Solution:
Suppose nA = known frequency = 100 Hz, nB = ? x = 5 bps, which remains unchanged after loading Unknown tuning fork is loaded so nB¯ Hence nA ? nB ¯ = x …
(i) nB ¯ ? nA = x …
(ii) From equation (i), it is clear that as nB decreases, beat frequency.
(i.e.
nA ? (nB)new) can never be x again.
From equation (ii), as nB¯, beat frequency (i.e.
(nB)new ? nA) decreases as long as (nB)new remains greater than nA, If (nB)new become lesser than nA the beat frequency will increase again and will be x.
Hence this is correct.
So, nB = nA + x = 100 + 5 = 105 Hz.
BETA
