In the circuit below, suppose the switch has been in position A for a very long time. If it is then switched to B at t=0, find the current as a function of time. A B + _ L R V

The force on a charge q moving with a velocity The magnitude of the force

left-hand rule right-hand rule

The angular velocity

The angular velocity (cyclotron frequency ) does not depend on velocity! The force is always perpendicular to velocity, so it cannot change the magnitude of the velocity, only its direction. The work done by the magnetic force is zero! Motion of a charged particle under the action of a magnetic field alone is always motion with constant speed.

Using Crossed and Fields Velocity selector independent of the mass of the particle!

Mass spectrometer

Small peace of wire

Ampere’s Law The field produced by an infinite wire

Biot-Savart Law Infinitesimally small element of a current carrying wire produces an infinitesimally small magnetic field (Also called Ampere’s principle) is called permeability of free space

Faraday’s Law of Induction The induced EMF in a closed loop equals the negative of the time rate of change of magnetic flux through the loop

There can be EMF produced in a number of ways: A time varying magnetic field An area whose size is varying A time varying angle between and Any combination of the above

R From Faraday’s law: a time varying flux through a circuit will induce an EMF in the circuit. If the circuit consists only of a loop of wire with one resistor, with resistance R, a current Which way? Lenz’s Law: if a current is induced by some change, the direction of the current is such that it opposes the change.

Third exam Tuesday, April Heldenfels Sections 807 and 808 start at 7 pm Sections 809 and 523 start at 8:15 pm

Help Session: When: tonight at 7:15 pm