Answer
The P point in the two-slit diffraction pattern is between the third $(m=3)$ and the fourth minimum $(m=4)$.
Work Step by Step
The angular locations of the diffraction minima are given by
$a\sin\theta=m\lambda$
or, $m=\frac{a\sin\theta}{\lambda}\;.........(1)$
In the part (a) of this question, we have calculated $\theta=0.173\;rad$
Substituting the known values in eq. 1, we obtain
$m=\frac{12\times10^{-6}\sin0.173}{600\times10^{-9}}$
or, $m=3.44$
The value of $m$ suggests that the angle corresponds to a point which is between the third $(m=3)$ and the fourth minimum $(m=4)$. In diffraction pattern, the maxima are not exactly midway between the minima.
Therefore, the P point in the two-slit diffraction pattern is between the third $(m=3)$ and the fourth minimum $(m=4)$.
