JEE MAIN 2020 NEWS
NATIONAL LEVEL ONLINE TEST
Electrostatics is the branch of physics that deals with the study of interactions between the stationary and slow-moving charges. Electric Force problems can be a bit tricky to solve. At first glance, these problems can seem to be scary and overwhelming to some students but no need to worry because this article is all about how you can easily solve electrostatics problems.
First of all, candidates need to read the problems or questions carefully so that they can identify all the known and unknown variables and this will be possible only if you have practiced and revised enough during your preparations. Moreover, candidates can expect one to two questions from this section in the examination. Go through the revision notes to earn your four marks from this section.
Electric changes are one of the fundamental physical properties of matter due to which it experiences a force when kept in the Electromagnetic field. Three types of changed particles are:
For an isolated system, the net charge of the system remains constant. Therefore charge cannot be created and cannot be destroyed.
Q = ne
e = 1.602 X 10-19 Coulomb
Question: Let us consider that a hollow metal sphere of radius 5 cm is charged so that the potential on its surface is 10 V. Calculate the potential at a distance of 2 cm from the center of the sphere?
Coulomb’s Law states that the force acting between the two charges is directly proportional to the product of the magnitude of the charges and inversely proportional to the square of the distance between them.
Coulombs can be represented by
Where is the constant of proportionality and is the permittivity of free space.
Vector Form of the Coulomb’s Law is
Question: Let us consider that Two equally charged spheres of radii a and b are connected together. Calculate the ratio of electric field intensity on their surfaces?
By using the superposition principle the force between the multiple charges can be found. According to the superposition principle, the net force on any charge due to multiple charges is the vector sum of all the forces acting on that charge due to the other charges are taken at a time. The individual forces remain unaffected due to other charges presence.
For n number of charges, the net resultant force due to the principle of superposition can be represented by
When a charge is continuously distributed over a surface of the conductor then it is known as Continuous Charge Distribution. The space and time of the charges in the continuous charge system is insignificant.
Line/ Linear Charge Distribution: When the charges are consistently spreaded over the length L of a conductor then it is called Line Charge Distribution. It is represented by λ.
λ = dq/dl Cm–1
Area/ Surface Charge Distribution: When the charge is consistently spread over the surface area of a conductor then it is known as Surface Charge Distribution. It is represented by σ
σ = dq/ds Cm–2
Volume Charge Distribution: When the charge is consistently distributed over the volume of a conductor then it is known as Volume Charge Distribution. It is represented by ρ
ρ = dq/dV Cm–3
Question: Which of the following figure shows the correct equipotential surfaces of a system of two positive charges?
Electric Filed: Electric Field is defined as the force experienced per unit positive test charge at a point when another charge is kept in the vicinity.
Electric Dipole and Electric Dipole Moment: Electric Dipole is a system of two equal in magnitude opposite changes that are separated by a very small distance.
Electric Dipole Moment is the product of charge and separation between them. It is a vector quantity.
Question: Let us consider that From a point charge, there is a fixed point A. At point A, there is an electric field of 500 V/m and a potential difference of 3000 V. Calculate the Distance between the point charge and A?
The number of electric lines of force crossing a surface normal to the area gives the electric flux ϕE
The electric flux through an elementary area ds is defined as the scalar product of area and field.
d ϕE = Eds cos θ
ϕE = ∫ E. ds
The electric potential at a point in a field is the amount of work done in bringing a unit positive charge from infinity to the point. It is equal to the Electric potential energy of unit positive charge at that point.
Electric Potential at a distance ‘d’ due to a point charge q in air or vacuum is represented by V.
It is a surface on which all points are at the same potential.
In the case of a Hollow Charged Sphere.
In the Case of Solid Charged Sphere
The potential at any point inside the sphere and at any point on its surface is the same
It is an equipotential surface. Outside the sphere, the potential varies inversely as the distance of the point from the centre.
Electron Volt is the unit of energy in particle physics and is represented as eV.
When a positive test charge is fired in the direction of an electric field the following occurs
A charged particle of mass m carrying a charge q and falling through a potential V acquires a speed of
Question: The expression E=−dv/dr implies that the electric field is in that direction in which
The electric line of force is the path along which a unit positive charge accelerates in the electric field and the tangent at any point to the line of force gives the direction of the field at that point.
Properties of Electric Lines of Force
The number of lines of force passing normally through a unit area around a point is numerically equal to E.
In a uniform field, lines of force are parallel to one another.
Difference between magnetic lines of force and electric lines of force
Dielectric Strength: Dielectric Strength is the minimum field intensity that should be applied to break the insulating property of the insulator.
The maximum charge that a sphere can hold totally depends on the size and dielectric strength of the medium in which the sphere is placed.
1. Question: Charge +q and -q are placed at points A and B respectively which are at a distance of 2L apart, C is the midpoint between A and B. Calculate the work done in moving a charge +Q along the semicircle CRD is
Tip to Solve the Question: First of all you have to calculator the values of potentials Vc and Vd, then you can calculate the work of work.
2. Question: If there is an infinite straight chain of alternating charges q and -q. It is given that the distance between the two neighboring charges is equal to a. Calculate the interaction energy of any charge with all the other charges.
Tip to Solve the Question: You can solve this question by using the formula
3. Question: The work done in placing a charge of 8×10−18coulomb on a condenser of capacity 100 microfarad is
Tip to Solve the Question: This question is direct and you can easily solve it if you remember the formula of Work Done that is W = Work done = ½ q2/C
Candidates can divide their remaining 45 days to the exam into weeks and make the best strategic plan to cover all the topics of JEE Main 2020. We have also prepared a study plan that you can apply or modify as per your convenience.
|Week 1||Pick two topics daily and give 1-hour each to each topic. Learn all the basics and other details of the topics. No need to pick the topics that you have left during the time of preparation.|
|Week 2||If you are still left with some topics then pick those topics and also quickly go through the revised topics again.|
|Week 3||Solve at least 30-40 questions within 1 to 2 hours. You can repeat the same activity 1 to 2 times a day.|
|Week 4||Pick one Topic and Identify the questions based on that topic from the previous years papers. Try to solve more number of questions to improve your speed.|
|Week 5||Since you are done with your revision again now you can take the Mock Tests daily.|
|Week 6||Go for Last and Final Revision.|
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