Question

A capacitor made of two circular plates each of radius $12\, cm$ and separated by $5\, mm$. The capacitor is being charged by an external source. The charging current is constant and equal to $0.15\, A$. The capacitance of the parallel plate capacitor is

• A. $40\,pF$
• B. $45\,pF$
• C. $70\,pF$
• D. $80\,pF$

Answer 1

Answer: (D)

$80\,pF$

Answer 2

Here, $= 12\, cm = 0.12\, m$ $d = 5 \,mm = 5 \times 10^{-3} \,m$, $\varepsilon_{0} = 8.85 \times 10^{-12}\, C_{2}\, N^{-1}\, m^{-2}$ Also, $A = \pi R^{2} = 3.14 \times \left(0.12\right)^{2}$ $m^{2} = 4.5 \times 10^{-2} \,m^{2}$ Capacitance, $C = \frac{\varepsilon_{0}A}{d}$ $= \frac{8.85 \times10^{-12}\times 4.5\times 10^{-2}}{5\times 10^{-3}}$ $= 79.65 \times 10^{-12} = 80\, pF$