Lenz's Law: Induced-Current Direction and Faraday-Law Applications

All flashcards

Lenz's law

The induced magnetic field opposes the change in magnetic flux that produces it.

Faraday's law for a one-turn loop

The induced-emf magnitude is $\varepsilon=\left|\frac{d\Phi_m}{dt}\right|$.

Increasing magnetic flux

The induced field acts to oppose the increase.

Decreasing solenoid current

The induced emf drives current in the same direction as the original current.

Lenz's law and energy conservation

Induced electrical energy requires work or another energy source.

Quiz questions

1. Viewed from the magnet, what current direction is induced when a south pole approaches a conducting loop?Answer: Clockwise
2. When current through a solenoid decreases, which direction does the induced current take?Answer: The same direction as the original current
3. What is the induced-emf magnitude for a coil with $N$ turns, each experiencing magnetic flux $\Phi_m$?Answer: $\varepsilon=N\left|\frac{d\Phi_m}{dt}\right|$
4. For a current loop, how does the right-hand rule relate the induced magnetic field to conventional current?Answer: Point the thumb along the field; curled fingers show the current direction.
5. Why does Lenz's law prevent induced electrical energy from appearing without an energy input?Answer: The induced response resists the change, so producing energy requires work or another source.