JEE Main Registration 2025 Session 1 (Open) - Link, Last Date, Fees, How to Apply

Electric Field Due To An Infinitely Long Charged Wire - Practice Questions & MCQ

Edited By admin | Updated on Sep 18, 2023 18:34 AM | #JEE Main

Quick Facts

  • 16 Questions around this concept.

Solve by difficulty

The electric field intensity due to a semi-infinite wire  at a point A which is at a distance of 10 cm as shown in the figure: 

(Given: charge density, \lambda = 3.0 \times 10^{-5} \frac{C}{m^2}    )

Concepts Covered - 1

Electric field due to an infinite line charge

Electric field due to an infinite line charge -

Let us assume that positive electric charge Q is distributed uniformly along a line, lying along the y-axis. We have to find the electric field at point D on the x -axis at a distance r_{0} from the origin. Let us divide the line charge into infinitesimal segments, each of which acts as a point charge; let the length of a typical segment at height l be dl. If the charge is distributed uniformly with the linear charge density \lambda, then the charge dQ in a segment of length dl is d Q=\lambda d l . At point D, the differential electric field dE created by this element is -

 

                                                                             

                                

                                                                    d E=\frac{d Q}{4 \pi \varepsilon_{0} r^{2}}=\frac{\lambda d l}{4 \pi \varepsilon_{0} r^{2}}=\frac{\lambda d l}{4 \pi \varepsilon_{0} r_{0}^{2} \sec ^{2} \theta}

                                                   \begin{array}{l}{\text { In triangle } A O D ; O A=O D \tan \theta, \text { i.e., } l=r_{0} \tan \theta} \\ \\ {\text { Differentiating this equation with respect to } \theta, \text { we get }} \\ \\ {\text { } \begin{array}{l}{dl=r_{0} \sec ^{2} \theta d \theta} \\ \\ {\text { Substituting the value of } d l} \\ \\ {\qquad d E=\frac{\lambda d \theta}{4 \pi \varepsilon_{0} r_{0}}}\end{array}}\end{array}

                                                   \begin{array}{l}{\text { Field } d E \text { has components } d E_{x} d E_{y} \text { given by }} \\ \\ {\qquad d E_{x}=\frac{\lambda \cos \theta d \theta}{4 \pi \varepsilon_{0} r_{0}} \text { and } d E_{y}=\frac{\lambda \sin \theta d \theta}{4 \pi \varepsilon_{0} r_{0}}}\end{array}

                                                   \begin{array}{l}{\text { If the wire has finite length and the angles subtended by }} \\ {\text { ends of wire at a point are } \theta_{1} \text { and } \theta_{2} \text { , the limits of integration }} \\ {\text { will be}} \\ {\qquad \begin{aligned} E_{x} &=\int_{-\theta_1}^{\theta_2} \frac{\lambda \cos \theta d \theta}{4 \pi \varepsilon_{0} r_{0}} \\ \\ &=\frac{\lambda}{4 \pi \varepsilon_{0} r_{0}}\left(\sin \theta_{1}+\sin \theta_{2}\right) \\ \\ E_{y} &=\int_{- \theta_{1}}^{+\theta_{2}} \frac{\lambda \sin \theta d \theta}{4 \pi \varepsilon_{0} r_{0}} \\ &=\frac{\lambda}{4 \pi \varepsilon_{0} r_{0}}\left(\cos \theta_{1}-\cos \theta_{2}\right) \end{aligned}}\end{array}

 

Special case-

1.If the line is infinite then the \\ \theta_1 = \theta_2 = 90^o

Putting the value, we get  - 

                                           E_x = \frac{\lambda}{2 \pi \varepsilon_or_o} 

                                          E_y = 0

2.If the line is semi-infinite then the \\ \theta_1 =0, and \ \theta_2 = 90^o

Putting the value, we get  - 

                    E_x = \frac{\lambda}{4 \pi \varepsilon_or_o}

                 E_y = \frac{\lambda}{4 \pi \varepsilon_or_o}

Study it with Videos

Electric field due to an infinite line charge

"Stay in the loop. Receive exam news, study resources, and expert advice!"

Get Answer to all your questions

Back to top