$\frac{1}{2} xPD X _5 x =\frac{1}{2} x _{3 x } X 4 x$
$\therefore PD =\frac{12 x }{5}$
$QD =\sqrt{( PQ )^2-( PQ )^2}=\sqrt{9 x ^2-\frac{144 x ^2}{25}}=\frac{9 x }{5}$
$\text { and } DR =5 x -\frac{9 x }{5}=\frac{16 x }{5}$
Magnetic field at $P$ due to current elements $P Q$ and $P R$ is zero as the point $P$ is on the conductor. Therefore, magnetic field at $P$ due to current element $QR$ is
$B=\frac{\mu_0 I }{4 \pi PD }\left(\sin \phi_1+\sin \phi_2\right)$
$B =\frac{\mu_0 I \times 5}{4 \pi \times 12 x }\left(\frac{(9 x / 5)}{3 x }+\frac{(16 x / 5)}{4 x }\right)$
$B =\frac{\mu_0 I }{48 \pi x }\left(\frac{3}{5}+\frac{4}{5}\right)$
$B =\frac{7 \mu_0 I }{48 \pi x } \cdot k =7$
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Statement $(I)$ : Dimensions of specific heat is $\left[\mathrm{L}^2 \mathrm{~T}^{-2} \mathrm{~K}^{-1}\right]$
Statement $(II)$ : Dimensions of gas constant is $\left[\mathrm{ML}^2 \mathrm{~T}^{-1} \mathrm{~K}^{-1}\right]$
$Reason$ : Relative velocity of $P$ w.r.t. $Q$ is the ratio of velocity of $P$ and that of $Q$.