Following are expressions for four plane simple harmonic waves
(i) \(\rm y_{1}=A \cos 2 \pi\left(n_{1} t+\frac{x}{\lambda_{1}}\right) \)
(ii) \(\rm y_{2}=A \cos 2 \pi\left(n_{1} t+\frac{x}{\lambda_{1}}+\pi\right)\)
(iii) \(\rm y_{3}=A \cos 2 \pi\left(n_{2} t+\frac{x}{\lambda_{2}}\right) \)
(iv) \(\rm y_{4}=A \cos 2 \pi\left(n_{2} t-\frac{x}{\lambda_{2}}\right)\)
The pairs of waves which will produce destructive interference and
stationary waves respectively in a medium, are
1
(iii, iv), (i, ii)
2
(i, iii), (ii, iv)
3
(i, iv), (ii, iii)
4
(i, ii), (iii, iv)