Faraday's Law
The induced emf equals the negative time rate of change of flux linkage. For N identical turns, flux linkage is N times the flux through one turn.
Why this shows up in the exam
Electric generators · Wireless charging · Dynamic microphones
Learn the idea
A changing magnetic flux produces an emf. A coil responds to change, not merely to the presence of a magnetic field. A strong constant field can produce zero emf, while a weaker rapidly changing field can produce more.
🧠 Memory hook: No change, no induction.
Get this one clearly and it pays off every single time it shows up in the paper. 🎯
Formulas & facts to keep ready
- emf = -N d(Phi)/dt — instantaneous induced emf
- |emf_avg| = N |Delta Phi|/Delta t — average magnitude over a time interval
How to approach it
- 1Find initial and final flux
- 2Compute flux change
- 3Divide by time and include N
Common slip-ups that cost marks
- •Using B instead of flux
- •Forgetting the number of turns
- •Using total time instead of the interval during which flux changes
🌟 That's the whole idea — you've got this. Try the practice set below; every question you attempt makes it stick a little harder.
Original chapter practice
Original questions for this chapter, not past-paper questions or an exact mapping to this individual concept.
A conducting rod of length 2 m moves at 3 m/s perpendicular to a 4 T magnetic field. Find the motional emf.
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Faraday's law explains how a changing magnetic field induces an electromotive force (EMF), while Lenz's law determines the direction of the induced current to oppose the change causing it.
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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.
Motional EMF
Motional EMF is the voltage induced in a conductor moving through a magnetic field, depending on the speed, length, and orientation of the conductor.