\(\Rightarrow\) \(I \propto {a^2}{n^2}\)
\(\Rightarrow\) \(\frac{{{I_1}}}{{{I_2}}} = {\left( {\frac{{{a_1}}}{{{a_2}}}} \right)^2} \times {\left( {\frac{{{n_1}}}{{{n_2}}}} \right)^2}\)
\( = {\left( {\frac{1}{2}} \right)^2} \times {\left( {\frac{1}{{1/4}}} \right)^2}\)
\(\Rightarrow {I_2} = \frac{{{I_1}}}{4}\)
$ {z_1} = A\sin (kx - \omega \,t) $ , $ {z_2} = A\sin (kx + \omega \,t) $ , $ {z_3} = A\sin (ky - \omega \,t) $ .