“The direction of an induced e.m.f. is always such that it tends to set up a current opposing the mo

Question

“The direction of an induced e.m.f. is always such that it tends to set up a current opposing the motion or the change of flux responsible for inducing that e.m.f.”, this is the statement for?

Examoogle · Accepted Answer

Lenz’s law

Explanation: Lenz's Law states that the direction of an induced electromotive force (e.m.f.) and the resulting induced current is such that it opposes the change in magnetic flux that produced it. This principle is a direct consequence of the Law of Conservation of Energy.

Working Principle: When a magnetic flux linked with a coil changes, an e.m.f. is induced. If the induced current were to reinforce the flux, it would lead to a perpetual increase in energy, which is impossible. Thus, the induced current creates its own magnetic field to counteract the original magnetic change (e.g., if a magnet approaches a coil, the coil produces a field to repel it).

Key Formulas: $\varepsilon = -\frac{d\Phi}{dt}$ — Faraday-Lenz law where the negative sign represents the opposition defined by Lenz's Law.

Key Points: Lenz's law obeys the Law of Conservation of Energy.; The negative sign in Faraday’s law of induction is the mathematical representation of Lenz's law.; It applies to both motional e.m.f. and transformer e.m.f.

Advantages: Ensures thermodynamic stability in electromagnetic systems.; Prevents creation of energy out of vacuum.; Allows for the damping effect in sensitive instruments like moving coil galvanometers.

Disadvantages: Requires external work to be done against the opposing force to induce current.; Often leads to Eddy current losses in electrical machinery (e.g., heating of transformer cores).

Applications: Induction motors and generators.; Eddy current brakes in trains.; Metal detectors and induction cooking surfaces.

Additional Info: Fleming's Right-Hand Rule is used to determine the direction of the induced current, whereas Lenz's Law explains the 'why' and the nature of the polarity.. Option A (Fleming's left hand) is for motor effect; Option B (Fleming's right hand) is for generator effect (direction determination); Option C (Faraday’s law) gives the magnitude.

Answer: D is correct — Lenz's law is the physical principle that states the induced e.m.f. always opposes the change in magnetic flux that caused it.

Exam Tip: Always remember that the negative sign in $e = -N \frac{d\Phi}{dt}$ is the specific mathematical notation for Lenz's Law.

Related Questions

Discussion (0)