Get plus subscription and access unlimited live and recorded courses

Last updated date: 19th Sep 2023

•

Total views: 140.7k

•

Views today: 3.39k

The chapter Electric Charges and Fields notes down some of the most important concepts of electric charges and fields for NEET, JEE, and other competitive exams. In the Electric Charges and Fields chapter, students will study the basic properties of electric charge, conductors, and insulators, and some laws related to them.

The chapter on Electric Charges and Fields begins with the very basic definition of Coulomb’s law, Electrostatic Forces, Dielectric, Electric Field, and what are different charge distributions helpful in studying the chapter ahead. These concepts will lead us to a very important part of the chapter, i.eVector notations of Electric Field, Electric Lines of Forces, Energy Density, and Electric Dipole.

The concepts mentioned above will help us in studying the chapter deeply along with the hands-on practice of many important numerical problems that will help us in acing the exams.

In this article, we will cover the important concepts and topics with the Electric Charges and Fields formulas as well as Electric Charges and Fields solutions for numericals that will help students to revise and boost their preparations for NEET and JEE.

Electric Charges and properties

Coulomb's Law

Electric Field

Conductors and Insulators

Dielectric

Electric Lines of Forces

Electric Flux

Electric Dipole

Gauss's Law

1. An electric dipole with a dipole moment $4 \times 10^{-9}$ C/m aligned at $30^{\circ}$ with the direction of a uniform electric field of magnitude $5 \times 10^{4}$N/C. Calculate the magnitude of torque acting on the dipole.

Sol:

Given,

Dipole moment p = $4 \times 10^{-9}$ C/m

E = $5 \times 10^{4}$N/C and angle = $30^{\circ}$

Torque = $\tau= \vec{p}\times \vec{E}$ = pEsin$\theta$

=$4 \times 10^{-9}$ $5 \times 10^{4}$ sin$30^{\circ}$

=$\times 10^{-4}$Nm is the correct answer.

Key point: Here, the formula of torque due to an electric dipole can be used directly.

2.Consider a uniform electric field E = $3 \times 10^{3}\hat{i}$N/C.

(a) What is the flux of this field through a square of 10 cm on a side whose plane is parallel to the yz plane(b) What is the flux through the same square if the normal to its plane makes a 60° angle with the x-axis?

Sol:

Given,

(a) E = $3 \times 10^{3}\hat{i}$N/C, side of square = 10cm = 0.1m

Area of square = 0.01m2.

Since the plane of square is parallel to the yz plane and the area vector is also in this plane so the angle between E and area vector is zero.

$\phi$= $\vec{E}.\vec{S}$

= $\phi$= $ \phi$= $\vec{E}\vec{S}\cos\theta$

= $3 \times 10^{3} \times 0.01 \cos 0^{\circ}$

=30 Nm2/C.

(b) $\phi$= $\vec{E}.\vec{S}$

= $\phi$= $ \phi$= $\vec{E}\vec{S}\cos\theta$

=$3 \times 10^{3}\times 0.01 \cos 60^{\circ}$

= **15** Nm2/C

Key point: Here, the formula of electric flux can be used directly.

1. Two parallel infinite line charges with linear charge densities +$\lambda$ C/m and -$\lambda$ C/m are placed at a distance of 2R in free space. What is an electric charge field midway between the two line charges? (NEET 2019)

Zero

$\dfrac{2 \lambda}{\pi \varepsilon_{\circ}R}$ N/C

$\dfrac{\lambda}{\pi \varepsilon_{\circ}R}$ N/C

$\dfrac{\lambda}{2\pi \varepsilon_{\circ}R}$ N/C

Sol:

Given,

As one can clearly see the linear charge distribution of parallel plates and the direction of $\vec{E}$ by both the plates on each other so the electric field due to plate 1 having linear charge density -$\lambda$ is

$\vec{E_{1}}$ = $\dfrac{\lambda}{2\pi \varepsilon_{\circ}R}\hat{i}$ N/C

Similarly the electric field due to plate 2 having linear charge density +$\lambda$ is

$\vec{E_{2}}$ = $\dfrac{\lambda}{2\pi \varepsilon_{\circ}R}\hat{i}$ N/C

As the Electric Field follows the vector superposition principle so the net $\vec{E}$ = $\vec{E_{1}}$ +$\vec{E_{2}}$

= $\dfrac{\lambda}{2\pi \varepsilon_{\circ}R}\hat{i}$ + $\dfrac{\lambda}{2\pi \varepsilon_{\circ}R}\hat{i}$

=$\dfrac{\lambda}{\pi \varepsilon_{\circ}R}\hat{i}$

Which is option (c)

Trick: The relationship between the Electric Field having $\lambda$ as linear charge density is $\vec{E}$ = $\dfrac{\lambda}{2\pi \varepsilon_{\circ}R}$.

2. Two point charges A and B, having charges Q and -Q respectively, are placed at a certain distance apart and the force acting between them is F. If 25% charge of A is transferred to B, then the force between charges becomes: (NEET 2019)

F

9F/16

16F/9

4F/3

Sol:

Given,

We have been provided two point charges A and B having charges +Q and -Q separated by distance r having force F between them.

Hence F = $\dfrac{KQ^{2}}{r^{2}}$

Now 25% of the charge is transferred from A to B then the charge left on A

$Q_A^\bracevert$ = Q- $\dfrac{Q}{4}$ = $\dfrac{3Q}{4}$

Similarly the charge on B now is

$Q_B^\bracevert$ = - Q+ $\dfrac{Q}{4}$ = $\dfrac{-3Q}{4}$

So the new forces due to $Q_A^\bracevert$ and $Q_B^\bracevert$

$F^{\bracevert}$ = $\dfrac{\dfrac{(3Q)}{4}^{2}}{r^{2}}$

$F^{\bracevert}$ = 9/16 $\dfrac{KQ^{2}}{r^{2}}$

Which is option (b)

Trick: Here, the formula of electrostatic force between two charge particles can be used directly.

1. A Conducting sphere of radius 10cm has an unknown Charge. If the Electric Field at a Point 20cm from the center of the sphere of magnitude 1.5×103 N/C is directed radially inwards, what is the net charge on the sphere?

(Ans: 6.67nC)

2. Four charges qA = 2 microcoulomb, qB = -5 microcoulomb,qC = 2 microcoulomb,qD = -5 microcoulomb are located at the corners of a square ABCD of side 10cm. What is the force on a charge of 1micro microcoulomb placed at the centre of a square?

(Ans: zero)

We conclude that the chapter electric charges and fields has many important concepts. In this article, we covered Electric Flux, Gauss’s Law and all other important concepts from the chapter along with solved and previous year questions. Students can test their knowledge with the help of practice questions.

See More

NEET 2023 exam date and revised schedule have been announced by the NTA. NEET 2023 will now be conducted on 7-May-2023, and the exam registration closes on last week of Dec 2022. You can check the complete schedule on our site. Furthermore, you can check NEET 2023 dates for application, admit card, exam, answer key, result, counselling, etc along with other relevant information.

See More

View All Dates

Application Form

Eligibility Criteria

Reservation Policy

Admit Card

NTA has announced the NEET 2023 application form release date on the official website https://neet.nta.nic.in/. NEET 2023 Application Form is available on the official website for online registration. Besides NEET 2023 application form release date, learn about the application process, steps to fill the form, how to submit, exam date sheet etc online. Check our website for more details.

Download full syllabus

Download full syllabus

View NEET Syllabus in Detail

All

Physics

Chemistry

Biology

See All

NEET 2023 free online mock test series for exam preparation are available on the Vedantu website for free download. Practising these mock test papers of Physics, Chemistry and Biology prepared by expert teachers at Vedantu will help you to boost your confidence to face the NEET 2023 examination without any worries.
The NEET test series for Physics, Chemistry and Biology that is based on the latest syllabus of NEET and also the Previous Year Question Papers.

See More

NTA is responsible for the release of the NEET 2023 cut off score. The qualifying percentile score might remain the same for different categories. According to the latest trends, the expected cut off mark for NEET 2023 is 50% for general category candidates, 45% for physically challenged candidates, and 40% for candidates from reserved categories. For the general category, NEET qualifying marks for 2022 ranged from 715-117 general category, while for OBC/SC/ST categories, they ranged from 116-93 for OBC, 116-93 for SC and 116-93 for ST category.

See More

The NEET 2023 result will be published by NTA on https://neet.nta.nic.in/ in the form of a scorecard. The scorecard will include the roll number, application number, candidate's personal details, and the percentile, marks, and rank of the candidate. Only those candidates who achieve the NEET cut-off will be considered qualified for the exam.

See More

Rank List

Counselling

Cutoff

NEET 2023 state rank lists will be released by the state counselling committees for admissions to the {state-quota-percentage} state quota and to all seats in private medical and dental colleges. NEET 2023 state rank lists are based on the marks obtained in entrance exams. Candidates can check the NEET 2023 state rank list on the official website or on our site.

Want to know which Engineering colleges in India accept the NEET 2023 scores for admission to Engineering? Find the list of Engineering colleges accepting NEET scores in India, compiled by Vedantu. There are 1622 Colleges that are accepting NEET. Also find more details on Fees, Ranking, Admission, and Placement.

See More

FAQ

**1. Is Electric Charges and Fields important for the JEE/NEET exam?**

Yes, the electric charges and fields chapter is one of the important chapters for JEE and NEET exams. It carries around 1-2 questions in NEET which carry around 2% marks. Due to the formula related questions from this chapter it becomes easy to solve and secure marks in the exams.

**2. Is the electric charges and fields chapter tough?**

No, the electric charges and fields chapter is easy to understand. If you understand the concepts discussed in this chapter, and practice related questions then you can successfully attempt the questions asked from this chapter in both NEET and JEE exams.

**3. Can I crack NEET by solving the previous years’ questions?**

According to experts, applicants who practice previous year's papers for JEE and NEET have a good probability of passing the exam. Anyway, practice is the key to success. Students must focus on solving methods and study conceptually along with the PYQ’s.

NEET News

NEET Blogs