An ac generator works on the laws of electromagnetic induction given by
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Faraday
In an ac generator, the rotating coil changes the magnetic flux through itself. By Faraday’s law of induction, this changing flux induces an alternating emf in the coil.
NCERT (2026-27):
AC Generator – “… From Faraday’s law, the induced emf for the rotating coil of N turns is then,
\( \displaystyle \varepsilon=-N\frac{d\Phi_B}{dt}=-NBA\frac{d}{dt}(\cos\omega t) \)”