Question

What is the magnitude of electric field intensity due to a dipole of moment $4 \times 10^{-8} C - m$ at a point distant $0.5 m$ from the center of dipole when line joining the point to the center of dipole makes an angle of $60^{\circ}$ with dipole axis?

• A. $4 \times 10^{-5} N / C$
• B. $5 \times 10^{-11} N / C$
• C. $2 \times 10^{7} N / C$
• D. $3.8 \times 10^{3} N / C$

Answer 1

Answer: (D)

$E =\frac{ P }{4 \pi \varepsilon_{ 0 } r ^{3}} \sqrt{3 \cos ^{2} \theta+1}$
$E =\frac{4 \times 10^{-8} \times 9 \times 10^{9}}{0.5 \times 0.5 \times 0.5} \times \sqrt{3(0.5)^{2}+1}$
$E =\frac{360}{0.125} \times \sqrt{1.75}$
$E =\frac{360 \times 1.32}{0.125}=3801.6$
$=3.8 \times 10^{3} N / C$