Question

A system has two charges $ q_A = 2.5 \times 10^{-7}C $ and $ q_B = -2.5 \times 10^{-7}C $ located at points $ A : (0, 0,- 15 \,cm) $ and $ B : (0, 0 + 15 \,cm) $ , respectively. What is the magnitude and direction of electric dipole moment of the system ?

• A. $ 7.5 \times 10^{-8}\, cm $ , from positive to negative charge
• B. $ 0.75 \times 10^{-8}\, cm $ , from negative to positive charge
• C. $ 7.5 \times 10^{-8}\, cm $ , from negative to positive charge
• D. $ 0.75 \times 10^{-8}\, cm $ , cm, from positive to negative charge

Answer 1

Answer: (C)

$q_{A}=2.5 \times 10^{-7}C$
$q_{B}=-2.5 \times 10^{-7}C$

Total charge o f the system, $q=q_{A}+q_{B}=0$
Distance between two charges at points $A$ and $B$,
$d=15+15=30\,cm=0.3\,m$
Electric dipole moment of the system is given by,
$p=q_{A}\times d=q_{B}\times d$
$=2.5 \times 10^{-7} \times 0.3$
$=7.5\times 10^{-8}\,cm$, along positive $z$-axis