Coulomb's law gives the electrostatic force between two point charges. For charges and separated by distance , the magnitude of the force each exerts on the other is , where , with the permittivity of free space ( in vacuum or air). Like Newton's law of gravitation, the force f
Electric Charges and Fields
Class 129 previous-year questions from this chapter every option and the correct answer, free · where the marks are
1. Coulomb's law and superposition
Exam focus: Force from multiple charges adds as vectors, not scalars — the net force on a charge comes from superposing each pairwise Coulomb force with its own direction, so just adding magnitudes fails whenever the charges aren't collinear.
Coulomb's Law and Force Between Multiple Charges
Physics Wallah - Alakh Pandey
Directly covers Coulomb's law and the superposition principle for multiple charges.
PhysicsNEET 2025show ▾Two identical charged conducting spheres A and B have their centres separated by a certain distance. The charge on each sphere is and the force of repulsion between them is . A third identical uncharged conducting sphere is brought in contact with sphere A first and then with B, and finally removed from both. The new force of repulsion between spheres A and B (the radii of A and B are negligible compared to the distance of separation, so they can be considered point charges) is best given as:
- A.
- B.
- C.
- D.✓
Solution
Touching A: the third sphere and A share , so A becomes . Touching B: it carries to B, which then holds . New force , i.e. .
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Save for spaced revision (free account)PhysicsNEET 2019show ▾Two parallel infinite line charges with linear charge densities and are placed at a distance of from each other in free space. What is the electric field midway between the two line charges?
- A.Zero
- B. N/C
- C. N/C✓
- D. N/C
The worked solution is part of a paid pack.
PhysicsNEET 2019show ▾Two point charges A and B, having charges and respectively, are placed at a certain distance apart, and the force acting between them is . If 25% of the charge of A is transferred to B, then the force between the charges becomes:
2. Electric field, field lines, dipole
Exam focus: On a dipole's axial line the field is 2kp/r³, but on its equatorial line it's only kp/r³ and points opposite to the dipole moment — both fall off as 1/r³, but the factor of 2 and the direction are what NEET swaps.
Electric Dipole: Field on Axis and Perpendicular Bisector
Physics Wallah - Alakh Pandey
Covers electric-dipole field derivations thoroughly; assumes electric-field basics from an earlier lecture and does not spend much time on generic field-line diagrams specifically.
PhysicsNEET 2023show ▾An electric dipole is placed at an angle of with an electric field of intensity . It experiences a torque equal to 4 N m. Calculate the magnitude of the charge on the dipole, if the dipole length is 2 cm.
- A.8 mC
- B.6 mC
- C.4 mC
- D.2 mC✓
The worked solution is part of a paid pack.
PhysicsNEET 2022show ▾Two point charges and are placed at a distance apart, as shown in the figure. The magnitude of the electric field intensity at a distance () varies as:
PhysicsNEET 2021show ▾A dipole is placed in an electric field as shown. In which direction will it move?
- A.Towards the left as its potential energy will increase
- B.Towards the right as its potential energy will decrease✓
- C.Towards the left as its potential energy will decrease
- D.Towards the right as its potential energy will increase
The worked solution is part of a paid pack.
3. Electric flux and Gauss's law with applications
Exam focus: Gauss's law counts only the charge enclosed by the surface — charges outside contribute zero net flux, though they still affect the field at points on it — and the field just outside a charged conductor is σ/ε0, twice an isolated sheet's σ/2ε0.
Gauss's Law: Concepts and Applications
Physics Wallah - Alakh Pandey
Comprehensive single lecture covering electric flux, Gauss's law and its applications with numericals.
PhysicsNEET 2023show ▾If over a surface, then:
- A.The number of flux lines entering the surface must be equal to the number of flux lines leaving it✓
- B.The magnitude of the electric field on the surface is constant
- C.All the charges must necessarily be inside the surface
- D.The electric field inside the surface is necessarily uniform
The worked solution is part of a paid pack.
PhysicsNEET 2020show ▾A spherical conductor of radius 10 cm has a charge of C distributed uniformly. What is the magnitude of the electric field at a point 15 cm from the centre of the sphere? ()
- A. N/C
- B. N/C✓
- C. N/C
- D. N/C
The worked solution is part of a paid pack.
PhysicsNEET 2019show ▾A hollow metal sphere of radius is uniformly charged. The electric field due to the sphere at a distance from its centre:
- A.Increases as increases, for and for
- B.Is zero as increases for , and decreases as increases for ✓
- C.Is zero as increases for , and increases as increases for
- D.Decreases as increases, for and for
The worked solution is part of a paid pack.