Today4/23 Magnetic Induction Review HW Questions? Exam 4/24

Force and motion of charged particles B-fields due to wires Force and Torque on current loops Forces from currents (like 4/16 Wires 2) Induced current (like 4/17)

Magnetic Induction

The current only flows while: the B-field is changing the ring is moving the magnet is moving

It’s all about a “changing” B field!!! Look at whether the # of field lines are

increasing or decreasing

Force on Current Loops

Ch 21: Force/Torque arises from a battery operated loop in a static B-field.

Ch 22: Current in loops “induced” by a “changing” external field. The loop then reacts as in Ch 21.

In fact, battery operated loops resist the changing field caused by themselves! Called “Self Induction” see 22.8

Faraday’s & Lenz’z Law

E = - t

is the # of field lines inside loop

Lenz’s Law

Loop “Voltage”

can change in many ways:changing B-fieldchanging loop areachanging loop anglechanging B-field angle

This is the “equation” you will see on the exam

E = - tUsing

Identify initial field direction Identify final field direction Determine direction of the “change” Use Lenz’s law to determine B-field due

to the current induced around the loop Use RHR #2 to find direction of induced

current

Energy Considerations

It takes energy to push current around a loop

Therefore, forces arising from induced currents must always serve to retard (or slow down) the object