AimMent
Exam level5 past questions

Eddy Currents and Applications

Eddy currents are circulating currents induced in conductors by changing magnetic fields, leading to energy loss and effects like electromagnetic damping.

Why this shows up in the exam

You need to know how eddy currents affect devices like transformers and how they are minimized.

How NEET tests this

Statement analysis · 3 QsApplicationDirect recall

Learn the idea

Eddy currents are loops of induced current that appear in any bulk conductor when the magnetic flux through it changes, and they always act to oppose that change (Lenz’s law). The key insight is that they arise from the induced emf, not from any pre‑existing electric potential.

🧠 Memory hook: Think of eddy currents like tiny whirlpools (eddies) forming in water when you stir it – the faster the stir (changing field), the stronger the whirlpools, and they always push back against your stir.

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

Formulas & facts to keep ready

  • Eddy currents are circulating currents induced in a conductor by a changing magnetic field (NCERT Class 12, Ch 6, §6.6).
  • The direction of the induced eddy current is such that its magnetic field opposes the change in the external flux (Lenz’s law).
  • Eddy‑current loss in a solid core varies as (B_max)² · t² · f², where t is the thickness of the material and f is the frequency of the alternating field.
  • Laminating the core (making it of thin insulated sheets) breaks the circulating paths and therefore reduces eddy currents and the associated loss.
  • Eddy currents produce heating and a damping force that can slow the motion of a magnet falling through a conducting loop.

How to approach it

  1. 1Read the statement carefully – does it involve a changing magnetic flux through a bulk conductor?
  2. 2Apply Lenz’s law: the induced eddy current will oppose the change, giving rise to heating or a retarding force.
  3. 3If the question is about transformer efficiency, recall that lamination is used to *reduce* eddy currents, not increase them.
  4. 4For quantitative loss, remember the proportionality to (B_max)² · t² · f² and that thinner laminations lower the loss.

Worked example — watch it click

Assertion (A): Eddy currents are produced in any metallic conductor when magnetic flux is changed around it. Reason (R): Electric potential determines the flow of charge.

  • A)Both (A) and (R) are true, and (R) is the correct explanation of (A).
  • ✅Both (A) and (R) are true, but (R) is not the correct explanation of (A).
  • C)(A) is true but (R) is false.
  • D)Both (A) and (R) are false.

The concept behind this problem

The worked example checks whether you know that eddy currents are produced solely by a changing magnetic flux (the assertion) and that the reason given – electric potential driving charge – is a true statement but unrelated to the cause of eddy currents.

Step by step

  1. 1Assertion about eddy currents is true.
  2. 2Reason about electric potential causing charge flow is also true but does not explain eddy current production, which is due to changing magnetic flux inducing emf.

Watch out

Students often mistake the true Reason as the explanation for the Assertion, linking electric potential to eddy‑current generation.

Common slip-ups that cost marks

  • •Confusing eddy‑current loss with hysteresis loss – they have different origins and different dependencies.
  • •Assuming that more eddy currents improve transformer efficiency; in reality they cause extra loss and lower efficiency.
  • •Ignoring the role of lamination – a solid core increases eddy currents, while a laminated core decreases them.

🌟 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 5

Statement I: A laminated core is used in transformers to increase eddy currents. Statement II: The efficiency of a transformer increases with increase in eddy currents.

Push further

More challenging

18 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 18

A strong bar magnet is moved rapidly towards a stationary wooden block. Which of the following statements is true regarding the interaction?

More from Electromagnetic Induction and Alternating Currents