Question

Two charges `+20muC and -20muC` are placed 10mm apart. The electric field at point P, on the axis of the dipole 10 cm away from its centre O on the side of the positive charge is

A. `8.6xx10^(9)NC^(-1)`
B. `4.1xx10^(6)NC^(-1)`
C. `3.6xx10^(6)NC^(-1)`
D. `4.6xx10^(5)NC^(-1)`

Answer 1

Correct Answer - C

Here, `q=pm20muC=pm20xx10^(-6)C,2a=10mm=10xx10^(-3)m`
`r=OP=10cm=10xx10^(-2)m`
`|vecp|=qxx2a=20xx10^(-6)xx10xx10^(-3)m=2xx10^(-7)m`
The electirc field along BP, `vecE=(2vecpr)/(4piepsilon_(0)(r^(2)-a^(2))^(2))`
As" " a lt lt r,
`vecE=(2|vecp|)/(4piepsilon_(0)r^(3))=(2xx2xx10^(-7)xx9xx10^(9))/((10xx10^(-2))^(3))=3.6xx10^(6)NC^(_1)`