Wave Motion 4 Question 18
17. Two identical straight wires are stretched so as to produce 6 beats/s when vibrating simultaneously. On changing the tension slightly in one of them, the beat frequency remains unchanged. Denoting by $T _1, T _2$ the higher and the lower initial tension in the strings, then it could be said that while making the above changes in tension
(1991, 2M)
(a) $T _2$ was decreased
(b) $T _2$ was increased
(c) $T _1$ was decreased
(d) $T _1$ was increased
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Answer:
Correct Answer: 17. (b, c)
Solution:
- $T _1>T _2$
$\therefore \quad v _1>v _2$
or $\quad f _1>f _2$
and $\quad f _1-f _2=6 Hz$
Now, if $T _1$ is increased, $f _1$ will increase or $f _1-f _2$ will increase. Therefore, (d) option is wrong.
If $T _1$ is decreased, $f _1$ will decrease and it may be possible that now $f _2-f _1$ become $6 Hz$.Therefore, (c) option is correct.
Similarly, when $T _2$ is increased, $f _2$ will increase and again $f _2-f _1$ may become equal to $6 Hz$. So, (b) is also correct. But (a) is wrong.
