Answer :

Let AB be a long thin wire of uniform linear charge density λ.

Let us consider the electric field intensity due to AB at point P at a distance h from it as shown in the figure.

The charge on a small length dx on the line AB is q which is given as q = λdx.

So, according to Coulomb’s law, electric field at P due to this length dx is

where, ϵ0 is the vacuum permittivity of the medium


This electric field at P can be resolved into two components as dEcosθ and dEsinθ. When the entire length AB is considered, then the dEsinθ components add up to zero due to symmetry. Hence, there is only dEcosθ component.

So, the net electric field at P due to dx is

dE' = dE cosθ



x = h tan θ

Differentiating both sides w.r.t. θ,

dx = h sec2θ dθ …………………….(2)

Also, h2 + x2 = h2 + h2tan2θ

h2 + x2 = h2(1+ tan2θ)

h2 + x2 = h2 sec2θ ………….(3)

(Using the trigonometric identity, 1+ tan2θ = sec2θ)

Using equations (2) and (3) in equation (1),


The wire extends from to since it is very long.

Integrating both sides,

This is the net electric field due to a long wire with linear charge density λ at a distance h from it.

NOTE: In the given case, it has been assumed that the length of the wire tends to infinity. In case of wires of finite lengths, the sin(θ) components cancel out only along the perpendicular bisector of the wire. At any other point, the net electric field will have both sin(θ) and cos(θ) components.

Rate this question :

How useful is this solution?
We strive to provide quality solutions. Please rate us to serve you better.
Try our Mini CourseMaster Important Topics in 7 DaysLearn from IITians, NITians, Doctors & Academic Experts
Dedicated counsellor for each student
24X7 Doubt Resolution
Daily Report Card
Detailed Performance Evaluation
view all courses

Five charges, q ePhysics - Exemplar

Fig. 1.10 represePhysics - Exemplar

The electric forcHC Verma - Concepts of Physics Part 2

A particle of masHC Verma - Concepts of Physics Part 2

The bob of a simpHC Verma - Concepts of Physics Part 2

A positive chargeHC Verma - Concepts of Physics Part 2

A rod of length LHC Verma - Concepts of Physics Part 2

Consider a uniforHC Verma - Concepts of Physics Part 2