Distance between the capacitor plates, \(d=5\;\text{cm}=0.05m\)
Radius of circular plate, \(r=12\;\text{cm}=0.12\;m\)
Constant charging current, \(I=0.15A\)
Permittivity of free space, \(\epsilon _o=8.85\times 10^{-12}C^2N^{-1}m^{-2}\)
Capacitance between the plates is given by
\(C=\dfrac{\mathit{\epsilon_o A}} d\)
Where,
\(A=\) Area of each circular plate \(=\pi r^2.\)
\(C=\dfrac{\epsilon _o\pi r^2} d\)
= \(\dfrac{8.85\times 10^{-12}\times \pi \times (0.12)^2}{0.05}\)
\(=8.0032\times 10^{-12}F=80.032\mathit{pF}\)
Charge on each plate, \(q=\mathit{CV}\)
Where,
\(V\) Potential difference across the plates
Differentiating it with respect to time \((t)\) gives:
\(\dfrac{\mathit{dq}}{\mathit{dt}}=C\dfrac{\mathit{dV}}{\mathit{dt}}\)
But, \(\dfrac{\mathit{dq}}{\mathit{dt}}\) = current \((I)\)
\(\dfrac{\mathit{dV}}{\mathit{dt}}\) = \(\dfrac I C\)
⇒ \(\dfrac{0.15}{80.032\times 10^{-12}}\) = \(1.87 × 10^9\;V / s\)
Therefore, the change in potential difference between the plates is \(1.87\times 10^9\ V/\mathit{s.}\)