Electrostatics Previous Year Questions — JEE Main Physics
79 past-year Electrostatics questions from JEE Main (Physics) — page 16.
Q44 (2026)
Two point charges of 1 nC and 2 nC are placed at the two corners of equilateral triangle of side 3 cm. The work done in bringing a charge of 3 nC from infinity to the third corner of the triangle is ____ $\mu\mathrm{J}$.
$\frac{1}{4\pi\epsilon_{0}}=9\times10^{9}\mathrm{N\cdot m^{2}/C^{2}}$
- $2.7$
- $5.4$
- $3.3$
- $27$
### Related Formula
$$W = q_3 \cdot V_{\text{system}}$$
$$V = \frac{kq_1}{r_1} + \frac{kq_2}{r_2}$$
### Core Logic
Work done is equal to the potential energy acquired by the 3 nC charge in the electric field of the other two charges.
{{SOL_IMG1}}
### Step 1: Formula Setup
$$W = \left( \frac{kq_1}{\ell} + \frac{kq_2}{\ell} \right) q_3$$
### Step 2: Value Substitution
$$q_1 = 1 \times 10^{-9} \mathrm{~C}$$
$$q_2 = 2 \times 10^{-9} \mathrm{~C}$$
$$q_3 = 3 \times 10^{-9} \mathrm{~C}$$
$$\ell = 3 \times 10^{-2} \mathrm{~m}$$
$$W = \frac{9 \times 10^9}{3 \times 10^{-2}} \left( 1 \times 10^{-9} + 2 \times 10^{-9} \right) \times 3 \times 10^{-9}$$
### Step 3: Final Calculation
$$W = 3 \times 10^{11} \times 3 \times 10^{-9} \times 3 \times 10^{-9}$$
$$W = 27 \times 10^{-7} \mathrm{~J} = 2.7 \times 10^{-6} \mathrm{~J} = 2.7 \,\mu\mathrm{J}$$
### Pattern Recognition
Factor out common terms ($k/\ell$) before substituting micro/nano orders to prevent simple arithmetic exponent errors.
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 12 Physics: Electrostatic Potential and Capacitance
Q35 (2026)
Identify the correct statements :
A. Effective capacitance of a series combination of capacitors is always smaller than the smallest capacitance of the capacitor in the combination.
B. When a dielectric medium is placed between the charged plates of a capacitor, displacement of charges cannot occur due to insulation property of dielectric.
C. Increasing of area of capacitor plate or decreasing of thickness of dielectric is an alternate method to increase the capacitance.
D. For a point charge, concentric spherical shells centered at the location of the charge are equipotential surfaces.
Choose the correct answer from the options given below.
- $\text{A, B and C only}$
- $\text{C and D only}$
- $\text{A, C and D only}$
- $\text{B and D only}$
### Core Logic
Let's analyze each statement:
Statement A: For a series combination, $\frac{1}{C_{\text{eq}}} = \frac{1}{C_1} + \frac{1}{C_2} + \dots$ This means $C_{\text{eq}}$ is always less than the smallest individual capacitance. This statement is correct.
Statement B: When a dielectric is placed in an electric field, macroscopic displacement of free charges doesn't happen, but microscopic 'displacement' (polarization) does occur. Charges bound to atoms slightly shift, creating bound surface charges. Thus, saying 'displacement of charges cannot occur' is strictly false in the context of polarization. The statement is incorrect.
Statement C: Capacitance $C = \frac{k \varepsilon_0 A}{d}$. Increasing area ($A$) or decreasing the thickness ($d$, which acts as plate separation if fully filled) increases the capacitance. This statement is correct.
Statement D: The potential of a point charge is $V = \frac{1}{4\pi\varepsilon_0} \frac{q}{r}$. For a constant $r$ (concentric spherical shells), $V$ is constant. This statement is correct.
### Step 1: Conclusion
Statements A, C, and D are correct.
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 12 Physics: Electrostatics
Q38 (2026)
Which one of the following is not a measurable quantity?
- $\text{Voltage difference}$
- $\text{Resistance}$
- $\text{Voltage}$
- $\text{Displacement current}$
### Core Logic
The term 'voltage' here implies absolute electric potential at a point. In physics, the absolute potential at any single point is meaningless on its own—it requires a reference point (usually taken as infinity for convenience). Thus, only the potential *difference* between two points can be directly measured experimentally.
### Step 1: Analyzing Options
Resistance, voltage difference (potential difference), and displacement current are all directly or indirectly measurable physical quantities. Absolute voltage (potential) is relative.
### Pattern Recognition
Like potential energy, absolute potential is arbitrary and unmeasurable without setting a reference baseline.
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 12 Physics: Electrostatics
Q41 (2026)
Identify the correct statements:
A. Electrostatic field lines form closed loops.
B. The electric field lines point radially outward when charge is greater than zero.
C. The Gauss-Law is valid only for inverse-square force.
D. The workdone in moving a charged particle in a static electric field around a closed path is zero.
E. The motion of a particle under Coulomb's force must take place in a plane.
Choose the correct answer from the options given below:
- $\text{A, B, D, E Only}$
- $\text{A, B, C, D Only}$
- $\text{B, C, D, E Only}$
- $\text{A, C, E Only}$
### Core Logic
Statement A: Electrostatic field lines never form closed loops. This indicates the conservative nature of the electrostatic field. (Incorrect)
Statement B: For $q > 0$, electric field lines point radially outward. (Correct)
Statement C: Gauss's Law fundamentally relies on the surface area of a sphere $4\pi r^2$ canceling the $1/r^2$ dependence of the force. If the force were not an inverse-square law, Gauss's theorem would not hold true. (Correct)
Statement D: Electrostatic force is conservative, meaning work done around any closed path is zero. (Correct)
Statement E: Coulomb's force is a central force. Motion under any central force always takes place in a plane (conservation of angular momentum direction). (Correct)
### Step 1: Final Evaluation
Statements B, C, D, and E are correct.
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 12 Physics: Electrostatics
