Initial intensity \\\\(=I_0\\\\) After \\\\(P_1\\rightarrow I_1=\\dfrac{I_0}{2}\\\\)After \\\\(P_3\\rightarrow I_2=I_1cos^245^o\\\\)\\\\(=\\dfrac{I_0}{2}\ imes \\dfrac{1}{2}\\\\)\\\\(=\\dfrac{I_0}{4}\\\\)After \\\\(P_2\\rightarrow I_3=I_2cos^245^o\\\\)\\\\(=\\dfrac{I_0}{4}\ imes \\dfrac{a}{2}=\\dfrac{I_0}{8}\\\\)