Consider a loop of radius $\text{'}r\text{'}$ between the two circular plates ,placed `maxially with them. Then area of the loop is  $A\text{'}=\pi r^2$
And area of the plate is  $A=\pi R^2$
By symmetry magnetic field induction $\overline{B}$ is equal in magnitude and is tangentially to tha circle at every point.
In this case , only displacement current $I_D$ will cross the loop. Therefore, using ampere’s Maxwell law, we have
 $\oint \overline{B}.\overline{dl}={\mu }_0{I}_D$
$\Rightarrow 2\pi rB={\mu }_0\times \left(\text{current passing through the area A'}\right)$ 
$\Rightarrow 2\pi rB={\mu }_{0}I\frac{\pi r^2}{\pi R^2}$ 
$$\begin{gathered} \Rightarrow B=\frac{{\mu }_0{I}_{D}r}{2\pi R^2} \\ \Rightarrow B=\frac{4\pi \times {10}^{-7}}{2\pi }\times \frac{15\times {10}^{-2}\times 1\times {10}^{-2}}{{\left({10}^{-1}\right)}^2} \\ \Rightarrow B=3\times {10}^{-8}T \end{gathered}$$