← Unit 5: Magnetism and Electromagnetic Induction
Magnetic Force & Faraday's Law
A moving charge in a magnetic field feels a force perpendicular to both its velocity and the field; a changing magnetic flux through a loop induces an EMF (Faraday's Law).
Overview
Magnetic force on a moving charge: F = qvBsinθ, direction given by the right-hand rule. Faraday's Law: induced EMF = -dΦ/dt, where Φ = B·A·cosθ is magnetic flux. Lenz's Law (the negative sign) says the induced current opposes the change in flux that created it.
Practice Quiz
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A bar magnet is pushed into a loop of wire, increasing the magnetic flux through it. By Lenz's Law, the induced current in the loop: