A parallel plate capacitor with circular plates of radius \(1~\text m\) has a capacitance of \(1~\text{nF}.\) At \(t = 0,\) it is connected for charging in series with a resistor \(R = 1~\text{M}{\Omega}\)$$ across a \(2~\text V\) battery (as shown in the figure). The magnetic field at a point \(P,\) halfway between the centre and the periphery of the plates, after \(t = 10^{–3}~\text s \) is: 
(the charge on the capacitor at the time \(t\) is \(q (t) = CV[1 – e^{(–t/ 𝜏 )}],\) where the time constant \(\tau\) is equal to \(CR.\))