Putting induction to work. The AC generator, a coil turning in a field, rods and frames moving in fields with resistors and capacitors, and the growth and decay of current in an LR circuit.
3 lessons, about 2 h3 simulations11 problems7 practice questionsPython in every lesson
Created by StemPy LabA coil turning at a steady rate in a magnetic field has the flux through each turn, so its emf is . The peak emf is , and the direction reverses twice in every turn. The driver must supply the torque that the field puts on the current, so the energy that goes out is the energy that comes in.
Every problem with a moving rod or frame is solved in four steps: the emf , the current , the force that opposes the motion, and then Newton's law or the energy. A falling rod reaches a terminal speed . A frame that crosses a field makes heat only while it enters and leaves. A capacitor in the circuit acts like extra mass.
When a battery is joined to a coil of inductance and resistance , the current grows as , with the time constant . When the battery is cut out, it dies away as . A current broken at once makes a huge emf, , and a spark. The energy is given back as heat.
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