In \( \varepsilon=-\displaystyle\frac{d\Phi_B}{dt} \), the negative sign is explained by which rule/law?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Lenz’s law
Faraday’s law gives the size of the induced emf as the rate of change of magnetic flux. The negative sign comes from Lenz’s law. By this law, the induced current opposes the change in magnetic flux that produces it.
NCERT (2026-27):
Lenz’s Law and Conservation of Energy – “… The polarity of induced emf is such that it tends to produce a current which opposes the change in magnetic flux that produced it. The negative sign shown in Eq. (6.3) represents this effect.”
\( \displaystyle \varepsilon=-\frac{d\Phi_B}{dt} \qquad (6.3) \)