$x =$ beat frequency $= 4 Hz,$ which is decreasing $(4→2)$
after increasing the tension of the string $y. $
Also tension of wire $y$ increasing so ${n_y} \uparrow $ ($ \because n \propto \sqrt T$)
Hence ${n_x} - {n_y} \uparrow = x \downarrow $ $\rightarrow$ Correct
${n_y} \uparrow - {n_x} = x \downarrow $ $\rightarrow$ Wrong
==> ${n_y} = {n_x} - x = 300 - 4 = 296Hz$
$y = a\sin (kx + \omega t)$ ......$(1)$
$y = a\sin (\omega t - kx)$ ......$(2)$
$y = a\cos (kx + \omega t)$ ......$(3)$
$y = a\cos (\omega t - kx)$ ......$(4)$
emitted by four different sources ${S_1},\,{S_2},\,{S_3}$ and ${S_4}$ respectively, interference phenomena would be observed in space under appropriate conditions when