Question

A spherical conductor of radius 10 cm has a charge of $3.2 \times 10^{-7} C$ distributed uniformly. What is the magnitude of electric field at a point $15\,cm$ from the centre of the sphere?
$(\frac {1}{4\pi \epsilon_o} = 9 \times 10^9 Nm^2/C^2)$

• A. $1.28 \times 10^4\,N/C$
• B. $1.28 \times 10^5\,N/C$
• C. $1.28 \times 10^6\,N/C$
• D. $1.28 \times 10^7\,N/C$

Answer 1

Answer: (B)

$1.28 \times 10^5\,N/C$

Answer 2

Electric field outside a conducting sphere
$E=\frac{1}{4\pi\varepsilon_{0}} \frac{Q}{r^{2}}$

$E=\frac{9\times10^{9}\times3.2\times10^{-7}}{225\times10^{-4}}$
$E=0.128\times10^{6}$
$E=1.28\times10^{5} N /C$

So, the correct option is (B): $1.28\times10^{5} N /C$