MCQ
Two tuning forks $A$ and $B$ give $4$ beats per second. The frequency of $A$ is $256 Hz$. On loading $B$ slightly, we get $5$ beats in $2$ seconds. The frequency of $B$ after loading is .... $Hz$
- A$253.5$
- B$258.5$
- ✓$260 $
- D$252 $
✓
Answer
Correct option: C.
$260 $
c
(c) $n_A$ = Known frequency$ = 256 Hz, n_B = ?$
$x = 4$ beats per sec which is decreasing ($4\, bps$ to $\frac{5}{2}bps$) after loading (i.e. $x\downarrow$)
Unknown tuning fork $B,$ is loaded so $ n_B\downarrow$
Hence $n_A -n_B\downarrow = x\downarrow$ ... $(i)$ $\rightarrow$ Wrong
$n_B\downarrow-n_A = x\downarrow$ ... $(ii)$ $\rightarrow$ Correct
$\Rightarrow$ $n_B = n_A + x = 256 + 4 = 260 Hz.$
(c) $n_A$ = Known frequency$ = 256 Hz, n_B = ?$
$x = 4$ beats per sec which is decreasing ($4\, bps$ to $\frac{5}{2}bps$) after loading (i.e. $x\downarrow$)
Unknown tuning fork $B,$ is loaded so $ n_B\downarrow$
Hence $n_A -n_B\downarrow = x\downarrow$ ... $(i)$ $\rightarrow$ Wrong
$n_B\downarrow-n_A = x\downarrow$ ... $(ii)$ $\rightarrow$ Correct
$\Rightarrow$ $n_B = n_A + x = 256 + 4 = 260 Hz.$
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