Electromagnetic induction is what happens when you move a magnet near a coil and electricity appears from nothing but motion. As the bar magnet sweeps through the coil the magnetic flux threading it rises and falls, and Faraday's law, EMF = −N·dΦ/dt, turns that change into a voltage — swinging the galvanometer needle. Watch it flip direction as the magnet passes through: coming in the current fights to push the magnet back, going out it pulls to hold it, the give-away sign of Lenz's law. Speed the magnet up or add turns of wire and the voltage climbs — the very principle behind every generator. It all runs on your device.
You are in the Physics lab.
Induced EMF over one full pass. The curve touches zero twice each half-swing — at the coil's center (flux greatest but momentarily steady, so dΦ/dx = 0) and at each turning point (magnet briefly at rest, so v = 0) — and flips sign at every crossing. The bright dot is the magnet's current position on the curve. It grows taller with faster motion, more turns or a stronger magnet.
What the magnet, the coil, the needle and the EMF curve are each telling you.
The bar magnet's field threads the loops of the coil, and the flux readout tracks how much passes through. It is largest when the magnet sits right in the middle of the coil and falls away as the magnet heads for either turning point — so the flux number rises to a maximum at the center and shrinks toward the ends. Nothing touches the wire; the coil feels the magnet through the field alone.
The induced EMF is −N·dΦ/dt, so it reflects how fast the flux is changing, not how large it is. That is why the reading and the green curve below drop to zero at two moments — right at the center (flux largest but momentarily steady) and at each turning point (the magnet is briefly at rest) — and swell to a peak in between. Watch the bright dot ride the curve as the galvanometer needle swings.
The minus sign is Lenz's law: the induced current always flows so as to oppose the change that made it. Approaching, the coil repels the magnet; leaving, it attracts it. So the current direction badge — and the needle — swing one way on the way in and flip the other way on the way out, which is why the EMF curve changes sign at every zero crossing.
A changing flux, a voltage from Faraday's law, and a direction set by Lenz's law.
A magnet at rest inside the coil induces nothing at all — only a changing magnetic flux drives a current. Sweeping the magnet through makes the flux threading the loops rise and fall, and it is that motion, through the field alone, that sets the whole effect going.
A changing flux drives a voltage around the coil equal to EMF = −N·dΦ/dt — the number of turns times the rate the flux changes. The change is fastest as the magnet sweeps past the coil's edge, so the EMF peaks there and reads zero at the center and the turning points. Try Fast motion, More turns or Strong magnet and watch the peak EMF and the curve grow taller.
The induced current always flows so as to oppose the change that made it — the meaning of the minus sign. Approaching, the coil repels the magnet; leaving, it attracts it. So the needle swings one way on the way in and the opposite way on the way out; reverse the motion and you reverse the current. It is the very principle behind every generator: spin it faster and the voltage climbs.
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Record induced EMF versus magnet speed and number of turns, and note direction changes.
A changing magnetic flux through a coil induces an EMF (Faraday’s law, EMF = -N·dΦ/dt). Faster changes and more turns give larger EMF, and Lenz’s law says the induced current opposes the change — the basis of generators and transformers.
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