A tuning fork arrangement (pair) produces $4$ beats/sec with one fork of frequency $288\, cps$. A little wax is placed on the unknown fork and it then produces $2\; beats/sec$. The frequency of the unknown fork is .... $cps$
AIEEE 2002, Medium
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(b) $n_A$ = Known frequency $= 288\, cps,$ $n_B = ?$
$x = 4 \,bps$, which is decreasing (from $4$ to $2$) after loading i.e. $x\downarrow$
Unknown fork is loaded so $n_B\downarrow$
Hence $n_A -n_B\downarrow = x\downarrow$ $\rightarrow$ Wrong
$n_B\downarrow -n_A\downarrow = x\downarrow$ $\rightarrow$ Correct
$n_B = n_A + x = 288 + 4 = 292 Hz.$
$x = 4 \,bps$, which is decreasing (from $4$ to $2$) after loading i.e. $x\downarrow$
Unknown fork is loaded so $n_B\downarrow$
Hence $n_A -n_B\downarrow = x\downarrow$ $\rightarrow$ Wrong
$n_B\downarrow -n_A\downarrow = x\downarrow$ $\rightarrow$ Correct
$n_B = n_A + x = 288 + 4 = 292 Hz.$
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