Electromagnetic Induction

📋 Teacher notes

• •Faraday's law: an EMF is induced in a circuit whenever the magnetic flux linking it CHANGES — no change, no EMF, even if the field itself is strong.
• •The size of the induced EMF depends on the RATE of change of flux — move the magnet faster, or use more turns, and the galvanometer deflects further.
• •Lenz's law gives the DIRECTION: the induced current always flows to OPPOSE the change that created it. An approaching magnet induces a current that makes the coil repel it; a receding magnet induces a current that makes the coil attract it back.
• •Lenz's law is really a statement of energy conservation — if the induced current instead ASSISTED the motion, you'd get free energy from nothing, which is impossible. The opposing force is exactly why you feel resistance pushing a magnet into a coil.
• •Undergraduate note: EMF = -N dΦ/dt is Faraday’s law in its general (integral) form; the minus sign IS Lenz’s law, encoded directly into the equation rather than argued separately.