Which one of the following statements is correct about Lenz's law?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → It is used to give the direction of induced current.
Faraday’s law gives the magnitude of the induced emf, and Lenz’s law gives its sign: the induced emf, and the current it drives in a closed circuit, is always in the direction that opposes the change in magnetic flux producing it. The minus sign expresses Lenz’s law.
\( \displaystyle \varepsilon = -\frac{d\phi_B}{dt} \)
Why the other options are incorrect
Option (1) It is used to give direction of force on current carrying conductor in a magnetic field. — Incorrect. The direction of the force on a current-carrying conductor in a magnetic field is given by Fleming’s left-hand rule.
Option (2) It is used to find the magnitude of an induced current. — Incorrect. The magnitude of the induced current comes from Faraday’s law, \( I = |\varepsilon|/R \).
Option (3) It is used to find the magnitude of an induced emf. — Incorrect. The magnitude of the induced emf is given by Faraday’s law, \( |\varepsilon| = |d\phi_B/dt| \).
NCERT (2026-27):
Lenz’s Law and Conservation of Energy – “In 1834, German physicist Heinrich Friedrich Lenz (1804-1865) deduced a rule, known as Lenz’s law which gives the polarity of the induced emf in a clear and concise fashion. The statement of the law is:
The polarity of induced emf is such that it tends to produce a current which opposes the change in magnetic flux that produced it.”