Electrostatic Potential, Potential Difference, Equipotential Surfaces, Capacitance, Parallel Plate Capacitor, and Energy Stored in a Capacitor are the key topics.
Revise capacitance formulas, energy stored in a capacitor, combination of capacitors, and dielectric-related equations.
Yes. It contains several numerical problems based on capacitors and electrostatic potential.
Generally 1–2 questions are asked in JEE Main.
Yes. They summarize formulas, concepts, and important exam topics for fast revision.
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Class 12 Physics Chapter 2: Electrostatic Potential and Capacitance
Electrostatic Potential and Capacitance is a fundamental chapter in electrostatics that covers electric potential, potential difference, capacitors, dielectrics, combinations of capacitors, and energy storage. These concepts form the foundation for current electricity and play a vital role in solving both conceptual and numerical problems in JEE Main and JEE Advanced.
ALLEN provides comprehensive theory for Class 12 Physics Chapter 2: Electrostatic Potential and Capacitance, along with key formulas, solved examples, PYQ insights, and expert exam tips to help students revise efficiently, master the chapter, and strengthen their preparation for JEE Main, JEE Advanced, and CBSE Board exams.
1.0Chapter Snapshot
Parameter
Details
Difficulty Level
Moderate to High
JEE Main Weightage
High (Generally 1–2 Questions)
JEE Advanced Weightage
High (2–4 Integrated Concepts)
Key Concepts Covered
Electric Potential, Potential Difference, Equipotential Surfaces, Capacitance, Capacitors, Dielectrics, Energy Stored in Capacitors
2.0Chapter 2 Smart Study Material by ALLEN Experts: Download PDFs
Continue your preparation by exploring these resources after completing Electrostatic Potential and Capacitance. These study materials will help reinforce concepts, improve problem-solving speed, and strengthen exam readiness.
Practice Resources
Chapter Mock Test Paper
Chapter Mock Test Solutions
JEE Main PYQs with Solutions
JEE Advanced PYQs with Solutions
JEE Important Questions & Solutions on Electrostatics
NEET Important Questions & Solutions on Electrostatics
Electric Potential And Capacitance
Electric potential is the potential energy per unit charge in an electric field, influenced by point charges, dipoles, and charged spheres. Capacitance is a conductor's ability to store charge, depending on its geometry and surrounding dielectrics. Capacitors store energy and can be combined in series or parallel to adjust total capacitance.e
1.0Definition Electric Potential
It is the work done by an external force to move a unit positive charge from a reference point to a given point without changing its kinetic energy.
Vp=q(W∞→p)ext (ΔK=0)
It is scalar quantity
Potential can be positive, negative and even zero
SI unit is joule/coulomb
2.0Electric Potential Due To a Point Charge
Electric potential at a point is the work done in bringing a unit positive charge from infinity to that point against the electric field, without changing its kinetic energy.
Electric potential at P due to +q charge, V1=xkq
Electric potential at P due to -q charge, V1=−xkq
Net electric potential V=V1+V2=0
Potential at general point (r,θ)
So, net potential at point A, V=r2k(pcosθ
V=r3k(p.r)Herer=OA
3.0Potential due to a Uniformly Charged Ring or Circular Arc
At the centre
V=RkQ
On its axis
V=4πε0(R2+2)21Q=R2+x2kQ=rkQ
Potential due to a Uniformly Charged Circular Arc
V=RkQ=Rk(θRλ)=kθλ
4.0Potential Due to a Uniformly Charged Sphere
Electric Potential due to a Charged Conducting Sphere
a. For outside points (r > R)
V=rkQ=ε0rσR2
b. For points on the surface (r = R)
V=ε0σR=RkQ
c. For Inside points (r < R)
V=rkQ
Variation of potential with r
Electric Potential due to Uniformly Charged Non-conducting Sphere
a. Outside (r > R)
V=rkQ
b. On the surface (r = R)
V=rkQ
c. Inside (r < R)
Vinside=2R3kQ[3R2−r2]
Variation of potential with r
5.0Relationship Between Electric Field and Electric Potential
F=−drdU
Dividing both sides by q
qF=−drd(qU)⇒E=−drdV(F=qEandU=qV)
E=−▽V
Ex=−∂x∂V, Ey=−∂y∂V, Ez=−∂z∂V
6.0Equipotential Surfaces
The locus of all such points which are at same potential or the surface at which potential of all the points are equal is known as equipotential surface (EPS). It can be of any shape.
Properties of equipotential surface
Electric field intensity is always perpendicular to EPS.
Work done in moving a charge from one point of EPS to another point of the same EPS is always zero.
Two EPS can never intersect each other.
EPS due to point charge - EPS of point charge is spherical in shape.
EPS due to line charge – EPS of line charge is cylindrical in shape.
EPS due to large plane charged sheet – EPS of a large plane sheet is plane in shape.
EPS due to unlike charges -
EPS due to like charges -
7.0Electric Potential Energy of a System of Charges
Electrostatic potential energy is the work done to bring a charge from infinity to its position without changing its kinetic energy.
Electrostatic Potential Energy (EPE) of two point charge system
ΔU=(W∞→r)ext=−∫∞rFext.dr
Ur−Uinfty=−∫∞rFext.dr=rkQq
(∴U∞=0)
U−0=rkQq
U=rkQq
8.0Electrostatic Potential energy of a three system of charge
US=U12+U23+U13
US=r12kq1q2+r23kq2q3+r13kq1q3
Note: For n point charges system
No. of pairs= 2n(n−1)
9.0Electrostatics of Conductors
Electric Field Inside a Conductor: The electric field inside a conductor in electrostatic equilibrium is zero.
Charge Distribution: Any excess charge on a conductor resides entirely on its surface.
Equipotential Surface: The entire conductor (including its surface) is at the same potential in electrostatic equilibrium.
Electric Field Just Outside the Surface: The field is perpendicular to the surface.
No Electric Field Parallel to the Surface: If there were, charges would move, contradicting equilibrium.
Cavity Inside a Conductor (No Charge):The electric field inside a cavity with no charge is zero, even if the conductor is charged.
Cavity with Internal Charge: Induced charges appear on the inner surface of the cavity to cancel the field inside the conductor.
Grounding: Connecting a conductor to the Earth allows excess charge to flow, maintaining zero potential.
10.0Properties of Conductors in Electrostatic Equilibrium
Conductors are materials which contain a large number of free electrons which can move freely inside the conductor.
Electrostatic field lines never exist inside a conductor.
Electric field lines terminate & originate always perpendicular to the surface of conductor because the surface of conductor is an equipotential surface.
Charge always resides on the outer surface of a conductor.
If there is a cavity inside a charged conductor with the cavity devoid of any charge then charge will always reside only on the outer surface of the conductor.
Electric field intensity near a conducting surface is given by,E=ε0σn^
When a conductor is grounded (earthed), its electric potential becomes zero. However, this doesn't always mean its charge is zero—only if the body is isolated can grounding ensure the charge is also zero.
11.0Electrostatic Shielding
It is the method of protecting a certain region from the effect of an electric field.
A cavity surrounded by conducting walls is a field free region as long as there are no charges inside the cavity.
Whatever be the charge and field configuration the field inside the cavity is always zero (Provided no charge present inside the cavity) This is known as electrostatic shielding.
Electrostatic shielding can be achieved by enclosing sensitive instruments in a hollow conductor.
Figure gives a summary of the important electrostatic properties of a conductor.
12.0Capacitance of a Conductor
It demonstrates a conductor's ability to store electrical energy through an electric field. If charge(Q) is given to an isolated conducting body and it's potential increases by V, then
⇒Q ∝ V , Q =CV
⇒=VQ (C= Capacitance of the capacitor)
Electrical capacitance is a Scalar quantity.
Capacitance of conductor depends upon shape, size, presence of medium and nearness of other conductor.
Graph Between Q and V
S I Unit- Farad
CGS Unit-Stat Farad
Dimensional Formula-[M-1L-2T4A2]
Combination of Capacitors
13.0Combination of Capacitors
Series Combination
Capacitors are connected end-to-end so that the same current flows through each Capacitor. The total Capacitance in series is less than any individual capacitor's Capacitance. The Charge on each Capacitor connected in series is the same.
When two capacitors are connected in series, then effective capacitance is given by
C1=C11+C21
C1=C1C2C1+C2
C=C1+C2C1C2
The effective capacitance of capacitors in series connection is lower than the capacitance of each capacitor individually.
The Charge for each capacitor in the series is the same.
Parallel Combination of Capacitor
Capacitors are connected across each other's terminals and share the same voltage. When a potential difference V is applied across the terminals all capacitors have equal potential difference. The equivalent Capacitance of parallel combination is more significant than any of the capacitances in the combination.
Effective Capacitance is given by, C=C1+C2+C3
Effective Capacitance of parallel combination is greater than any of the capacitance.
In Parallel combination, voltage across each Capacitor is the same.
Parallel Plate Capacitor(PPC)
It comprises two large, flat, parallel conducting plates separated by a small distance.
C=dε0A
Capacitance of parallel plate capacitor with dielectric
C=dε0εrA=εrC0(∴C0=dε0A)
Capacitance of Parallel Plate Capacitor Depends on
Area ⇒C∝A
Distance between the plates ⇒C∝d1
Medium between the Plates ⇒C∝εr
Capacitance of Isolated Spherical Conductor
If the medium around the conductor is vacuum or air than capacitance is given by, C=4πϵ0R (∴R = Radius of Spherical Conductor(Solid or Hollow)
If the medium around the conductor is a dielectric of constant K from surface of sphere to infinity then Cmedium=4πε0KR
Cair/vacuumCmedium=K=Dielectric Constant
Capacitance of Spherical Capacitor
Case 1: Outer Sphere is Earthed
When a charge Q is given to the inner sphere it is uniformly distributed on its surface A charge –Q is induced on the inner surface of the outer sphere. The charge +Q induced on the outer surface of the outer sphere flows to earth as it is grounded.
E=0 For r<a and E=0 for r>b ,this arrangement is known as spherical capacitor
Capacitance of spherical capacitor is given by C=b−a4πε0ab
If dielectric medium is filled then C=b−a4πε0εrab
Case 2: Inner Sphere is earthed
Capacitance is given by, C=b−a4πε0b2
Cylindrical Capacitor
There are two coaxial conducting cylindrical surfaces where l >> a and l >> b, where a and b are the radius of cylinders. When a charge Q is given to the inner cylinder it is uniformly distributed on its surface. A charge –Q is induced on the inner surface of the outer cylinder. The charge +Q induced on outer surface of outer cylinder flows to earth as it is grounded. Hence Capacitance is given byC=ln(ab)2πε0l
14.0Dielectrics and Their Effect on Capacitance
Capacitors with Dielectric
Electric Field in the absence of Dielectric, E=ε0σ
Electric Field in the absence of Dielectric,E0=ε0AQ
Electric Field in absence of Dielectric, E=dV
Capacitance in absence of Dielectric, C0=V0Q
Capacitance in presence of Dielectric, C=VQ−Qb
Dielectric Constant or Relative Permittivity (K or εr)
K=ϵ0ϵ=EE0=VV0=C0C=Q−QbQ=σ−bσ
In presence of dielectric, capacitance is increased by a factor K
C=dϵ0AK=KC0
Capacitance of Parallel plate Capacitor when dielectric is partially filled
Capacitance is given by, C=(d−t)+ϵrtϵ0A
15.0Effects of Dielectrics in Capacitor
Distance Division
Distance is Divided and area remains same
Capacitors are in Series
Individual Capacitance are C1=d1ϵ0ϵr1A and C2=d2ϵ0ϵr2A
Effective Capacitance is given by, C=ϵ0A[d1ϵr2+d2ϵr1ϵr1ϵr2]
Special Case: If d1=d2=2d⇒C=dϵ0A[ϵr1+ϵr22ϵr1ϵr2]
Area Division
Area is divided and distance remains same
Capacitors are in Parallel
Individual capacitors are
C1=dϵ0ϵr1A1C2=dϵ0ϵr2A2
Effective Capacitance is given by C=dϵ0ϵr1A1+dϵ0ϵr2A2
Special Case: If A1=A2=2A⇒C=dϵ0A(2ϵr1+ϵr2)
16.0Energy Stored in a Capacitor
A capacitor is a device designed to store electrical energy. The process of charging a capacitor entails transferring electric charges from one plate to another. The work done during this charging process is stored as electrical potential energy within the capacitor.
V=qW=dqdW
dW=Vdq=Cqdq
W=∫dW=∫0QCqdq=C12Q2=2CQ2
U=2CQ2=21CV2=21QV
17.0Sample Questions on Electric Potential and Capacitance
Q-1. A conducting sphere of radius R has electric field E at distance 3R from the centre. Find potential difference between the centre of the sphere & the point where the electric field is E.
Solution:
E=(3R)2kQ=9R2kQ⇒kQ=9ER2
VCentre=RkQ=R9ER2=9ER
VP=rkQ=3R9ER2=3ER
VCentre−VP=9ER−3ER=6ER
Q-2. Find potential at points A,B and C due to the given arrangement of shells.
Solution:
VA=akQ1+bkQ2
VB=akQ1+bkQ2
VC=bkQ1+bkQ2
Q-3. A charge in moving via three paths, 1, 2, and 3. as shown in figure. Find work done in each case.
Solution: Potential at points A, B, C and D is V=Rkq. All the points are equipotential points, so work done in each case is zero.
Q-4. Calculate potential due to a charge 5×10−7 C at a point P located 9 cm away. Also find work done in bringing an another charge of 3×10−8 C from infinity to the point.
Before attempting numerical questions, quickly revise these essential formulas:
Electric Potential due to a Point Charge
Electric Potential due to Multiple Charges
Electric Potential due to an Electric Dipole
Relation between Electric Field and Potential
Capacitance Formula
Parallel Plate Capacitor
Series Combination of Capacitors
Parallel Combination of Capacitors
Energy Stored in a Capacitor
Energy Density of Electric Field
3.0High Weightage Topics
The following topics have consistently appeared in JEE Main and JEE Advanced examinations and should be given higher priority during revision.
Topic
Focus Area
Electric Potential
Point charge, multiple charges
Potential Difference
Work done and conservative electric field
Equipotential Surfaces
Properties and field relationship
Potential due to Electric Dipole
Axial and equatorial positions
Capacitance
Parallel plate capacitor
Capacitor Combination
Series and parallel combinations
Dielectric Materials
Effect on capacitance and electric field
Energy Stored in Capacitors
Charging and discharging numericals
4.0Formula Handbook
The following formulas are the most important for solving JEE Main and JEE Advanced questions from Electrostatic Potential and Capacitance.
Related Videos
5.0Common Mistakes & JEE Tips
Electrostatic Potential and Capacitance is a concept-driven chapter where students often lose marks due to incorrect sign conventions, improper capacitor combinations, and confusion between electric potential and potential energy. Avoiding these mistakes can significantly improve your accuracy in JEE Main and JEE Advanced.
Common Mistake
Correct Approach
Confusing Electric Potential with Potential Energy
Electric Potential is energy per unit charge, whereas Potential Energy depends on the value of the charge.
Ignoring the sign of electric potential
Electric potential is an algebraic quantity; always consider the sign of the source charge.
Incorrect capacitor combinations
Use the correct formulas for series and parallel combinations.
Assuming capacitance depends on charge
Capacitance depends only on geometry and dielectric material.
Forgetting the effect of dielectrics
Dielectric materials increase capacitance and reduce the effective electric field.
Using incorrect energy formula
Select the appropriate energy expression based on the given variables.
Mixing electric field and electric potential concepts
Electric field is the negative gradient of electric potential.
Incorrect SI unit conversion
Always use SI units such as Volt (V), Farad (F), Coulomb (C), and Joule (J).
ALLEN Faculty Tips
Draw neat capacitor diagrams before solving numerical problems.
Memorize standard formulas for series and parallel capacitor combinations.
Understand the physical meaning of electric potential instead of memorizing formulas blindly.
Revise dielectric concepts thoroughly as they are frequently asked in JEE.
Practice previous years' questions on capacitor combinations and energy stored.
Revise important formulas regularly to improve speed and accuracy.
6.0PYQ Trend Analysis
Electrostatic Potential and Capacitance is one of the highest-weightage chapters in Class 12 Physics for both JEE Main and JEE Advanced. Questions are primarily numerical and concept-based, with a strong emphasis on electric potential calculations, capacitor combinations, dielectric materials, and energy stored in capacitors.
Note: The trend below is based on the analysis of previous years' JEE Main and JEE Advanced question papers. The exact number of questions may vary each year.
Concept
Questions Asked (Last 5 Years)
Average Difficulty
Electric Potential
5–6
Easy–Moderate
Potential Difference
3–4
Moderate
Equipotential Surfaces
2–3
Easy
Capacitance
7–8
Moderate
Capacitor Combinations
5–6
Moderate
Dielectric Materials
3–4
Moderate
Energy Stored in Capacitors
5–6
Moderate
Most Common Question Types
Electric potential due to point charges and charge distributions.
Work done in moving a charge between two points.
Relation between electric field and electric potential.
Series and parallel capacitor combinations.
Dielectric insertion problems.
Energy stored in capacitors.
Assertion–Reason and concept-based MCQs.
Smart Revision Strategy
If you're short on time, revise the chapter in the following order: