Physic Labs

Electricity and magnetism

Faraday–Lenz electromagnetic induction

Explore ε = −N dΦ₁/dt: the rate of flux change and coil turns affect emf, while the minus sign expresses Lenz's law. Measure induced emf as flux changes, then verify ε=−N dΦ/dtε = −N\,dΦ/dt.

High school

⚠ The induction simulation is virtual; keep real magnets away from sensitive electronics and implanted medical devices.

Equipment

  • Magnet moving along the coil axis, draggable and reversible
  • Speed v and coil-turn N sliders; emf and current meters

Procedure

  1. Change speed and direction of motion

    Let the simulation run and watch the emf ε and current I meters as the magnet approaches and then recedes from the coil. Increase speed v and compare the deflection; raise the turns N to see a stronger signal. Press Reverse pole or drag the magnet to reverse the flux change, then check that ε and I change sign in accordance with Lenz's law. Compare the observed quantities with ε=−N dΦ/dtε = −N\,dΦ/dt.

  2. Check the induced emf

    Keep the direction of motion fixed, vary magnet speed and then turn count N. Record the emf reading and compare with ε=−N dΦ/dt\varepsilon = -N\,d\Phi/dt; a faster flux change produces a larger emf magnitude.

  3. Check the sign using Lenz's law

    Reverse the magnet pole or its direction of motion, then compare the signs of ε and I on the meters. Record the flux-change direction and explain why induced current opposes the change that produces it. Compare the observed quantities with ε=−N dΦ/dtε = −N\,dΦ/dt.

Simulation

Experiment history

Michael Faraday, the English experimentalist, discovered electromagnetic induction in 1831 after observing current in a coil when the magnetic field changed. He investigated moving magnets, coils, and circuits, and developed the idea of “lines of force” to describe fields. Joseph Henry discovered induction independently at about the same time; their findings helped make electric generators possible. Faraday found that induced emf depends on how rapidly magnetic flux through a circuit changes. In 1834 Heinrich Lenz stated that the induced current acts to oppose the change that produces it, represented by the minus sign in Faraday–Lenz law. For a coil of N turns, ε = −N dΦ/dt; the sign depends on the chosen normal and current directions, not simply on whether a magnet moves inward or outward.

Related physicists

Michael FaradayHeinrich LenzJoseph Henry

Related library topics

Electromagnetic induction, Faraday–Lenz law