PhysicsElectromagnetic inductionClass 12

Electromagnetic induction: interactive simulation

A changing magnetic flux through a coil drives a current around it. It does not matter whether the magnet moves, the coil moves or the field itself changes — only the rate of change of flux counts.

Useful for: JEE Main, JEE Advanced, NEET, CBSE Boards, AP Physics C: E&M, A-level Physics, IB Physics · 4 modes in one lab

What you can explore

  1. 1

    Magnet & coil (Lenz)

    Drag a magnet near a coil, see the induced pole, galvanometer deflection and EMF trace.
  2. 2

    Motional EMF

    A rod sliding on rails in a magnetic field: EMF, current direction, braking force and power.
  3. 3

    LR circuit

    Growth and decay of current, time constant L/R and stored energy.
  4. 4

    AC generator

    Rotating coil, flux and EMF against time, peak and rms EMF.

Try this

Push a magnet in and out and watch which way the coil fights back, slide a rod along rails and feel the magnetic brake, switch on an inductor and see the current refuse to jump, then spin a coil to make AC.

  1. 1

    Push the north pole towards the coil, then pull it away.

    What you should see

    Approaching: the near face becomes N and repels. Receding: it becomes S and attracts. The needle swings opposite ways.

  2. 2

    Hold the magnet still right next to the coil.

    What you should see

    The EMF is zero — the flux is large but not changing.

  3. 3

    In Motional EMF, use B = 0.5 T, l = 0.5 m, v = 4 m/s, R = 2 Ω.

    What you should see

    ε = 1 V, I = 0.5 A, braking force 0.125 N, and the power you supply (0.5 W) equals the heat in R.

  4. 4

    In LR circuit, use E = 10 V, R = 5 Ω, L = 2 H and close the switch.

    What you should see

    τ = 0.4 s. The current reaches 63.2 % of 2 A at t = τ and stores ½LI² = 4 J when full.

  5. 5

    In AC generator, use 100 turns, 0.1 T, 0.02 m² at 3000 rpm.

    What you should see

    ω ≈ 314 rad/s, peak EMF ≈ 62.8 V, rms ≈ 44.4 V at 50 Hz.

Formulas behind it

Faraday’s law

ε=−NdΦBdt\varepsilon = -N\frac{d\Phi_B}{dt}

Motional EMF

ε=Bvl\varepsilon = Bvl

Magnetic braking force

F=BIl=B2l2vRF = BIl = \frac{B^2l^2v}{R}

Current growth in an LR circuit

i(t)=ER(1−e−t/τ),τ=LRi(t) = \frac{E}{R}\left(1 - e^{-t/\tau}\right),\quad \tau = \frac{L}{R}

Energy stored in an inductor

U=12LI2U = \tfrac{1}{2}LI^2

AC generator

ε=NBAωsin⁡ωt\varepsilon = NBA\omega\sin\omega t

Common mistakes

  • Forgetting the minus sign’s meaning: the induced EMF opposes the change in flux, not the flux itself.
  • Thinking a strong stationary magnet induces a current.
  • Expecting the current in an inductor to change instantly when a switch is closed or opened.
  • Saying the generator EMF is maximum when the coil faces the field. It is maximum when the coil’s plane is parallel to B.
Practise 153 questionsCheck your answer instantly, with a worked solution.Stuck on a electromagnetic induction question?Snap it and get a whiteboard video solution.

FAQ

Why is Lenz’s law a consequence of energy conservation?

If the induced current helped the change instead of opposing it, the magnet would speed up by itself and create energy from nothing.

What are eddy currents?

Loops of induced current inside a solid conductor in a changing field. They cause heating and braking, which is why transformer cores are laminated.

What is the unit of inductance?

The henry (H): a coil has 1 H when a current changing at 1 A/s induces 1 V across it.

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