Question

A parallel-plate capacitor has circular plates of radius $8\, cm$ and plate separation $1\, mm$. What will be the charge on the plates if a potential difference of $100\, V$ is applied?

• A. $1.78 \times 10^{-8} C$
• B. $1.78 \times 10^{-5} C$
• C. $4.3 \times 10^{4} C$
• D. $2 \times 10^{-9} C$

Answer 1

Answer: (A)

$C=\frac{\varepsilon_{0} A}{d} =\frac{8.85 \times 10^{-12} \times 3.14 \times 0.08 \times 0.08}{1 \times 10^{-3}}$
$q=C V =\frac{8.85 \times 10^{-12} \times 3.14 \times .08 \times .08 \times 100 V }{1 \times 10^{-3}}$
$=1.78 \times 10^{-8} C$