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Foundation4 past questions

Electrostatic potential and potential energy

Explore the concept of electric potential, its relation to electric field, work done in moving charges, and potential energy in electrostatics.

Why this shows up in the exam

You must relate potential, field, and energy to solve NEET problems involving work and energy in electrostatics.

How NEET tests this

Direct recall · 2 QsStatement analysisNumerical

Learn the idea

Electric potential at a point is the work per unit positive charge required to bring it from infinity, and the associated potential energy is simply q × V. The key insight is that potentials from many charges add algebraically (superposition) while fields add vectorially.

🧠 Memory hook: Think of potential as the height of a hill (energy per unit charge) and the electric field as the slope of that hill – the steeper the slope, the stronger the field.

Get this one clearly and it pays off every single time it shows up in the paper. 🎯

Formulas & facts to keep ready

  • Electric potential V = work done by external agent per unit charge = –∫∞→r E·dl
  • Potential due to a point charge V = (1/4πϵ₀)·(q/r)
  • Potential energy U = q V and ΔU = –W_by_field
  • Equipotential surfaces are everywhere perpendicular to electric field lines
  • Electric field E = –∇V (magnitude E = –dV/dr along a line)
  • Potential is a scalar – signs of charges matter directly in V

How to approach it

  1. 1Identify all charges that contribute to the point of interest
  2. 2Write the scalar potential of each charge using V = kq/r and add them (superposition)
  3. 3Multiply the total V by the test charge q₀ to obtain the work done (or potential energy)
  4. 4If the question asks about direction of field or equipotentials, use E = –∇V → field is normal to equipotential surface

Worked example — watch it click

Assertion A: Electric potential of the earth is taken to be zero. Reason R: No electric field exists on the earth's surface.

  • A)If both assertion and reason are true, and reason is the correct explanation of assertion.
  • B)If both assertion and reason are true, but reason is not the correct explanation of assertion.
  • ✅If assertion is true but reason is false.
  • D)If both assertion and reason are false.

The concept behind this problem

The worked example checks whether you know that the Earth’s zero potential is a chosen reference, not a consequence of a vanishing electric field at its surface.

Step by step

  1. 1Assertion: Earth's potential is conventionally taken as zero reference point.
  2. 2TRUE (by convention).
  3. 3Reason: Electric field does exist on Earth's surface (atmospheric electric field ~100 V/m, fields from charges, etc.).
  4. 4FALSE.
  5. 5The assertion is true by convention for convenience in defining potential reference, not because of absence of electric field.

Watch out

Students often equate ‘zero potential’ with ‘no electric field’, leading them to mark the reason as true.

Common slip-ups that cost marks

  • •Confusing work done by the external agent (positive) with work done by the field (negative)
  • •Ignoring the sign of each charge when adding potentials – a negative charge gives negative V
  • •Assuming that a zero reference potential (e.g., Earth) implies the electric field there is zero

🌟 That's the whole idea — you've got this. Try the practice set below; every question you attempt makes it stick a little harder.

Practise it

These are real questions from past NEET papers that test this exact idea.

Question 1 of 4NEET 2022

Six charges +q, -q, +q, -q, +q and -q are fixed at the corners of a hexagon of side d as shown in the figure. The work done in bringing a charge q₀ to the centre of the hexagon from infinity is (ε₀ = permittivity of free space): +q -q q₀ d +q -q +q -q

Push further

More challenging

4 harder questions built from the past papers above — a step up in difficulty, with distractors designed so you can't get there by elimination. Written and checked by our reviewers, not from a real paper.

Question 1 of 4

Assertion A: The electric potential at the center of a uniformly charged non-conducting sphere is higher than its surface potential. Reason R: The electric field inside a uniformly charged non-conducting sphere is zero.

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