Physics for Scientists and Engineers II, Summer Semester Lecture 14: June 22 nd 2009 Physics for Scientists and Engineers II

Physics for Scientists and Engineers II, Summer Semester Magnetism in Matter We now know how to build “electromagnets” (using electric current through a wire). We also found that a simple current loop produces a magnetic field / has a magnetic dipole moment. How about the “current” produced by an electron running around a nucleus? Let’s use a classical model (electron is a point charge orbiting around a positively charged nucleus. - + direction of motion of electron The tiny current loop produces a magnetic moment Orbital angular momentum of electron

Physics for Scientists and Engineers II, Summer Semester Magnetism in Matter - + L = “orbital angular momentum”

Physics for Scientists and Engineers II, Summer Semester Quantization

Physics for Scientists and Engineers II, Summer Semester Spin

Physics for Scientists and Engineers II, Summer Semester Diamagnetism + magnetic moments cancel each other

Physics for Scientists and Engineers II, Summer Semester Diamagnetism + Net magnetic moment exists in the direction OPPOSITE to the magnetic field.

Physics for Scientists and Engineers II, Summer Semester Paramagnetism

Physics for Scientists and Engineers II, Summer Semester Ferromagnetism

Physics for Scientists and Engineers II, Summer Semester Faraday’s Law of Induction

Physics for Scientists and Engineers II, Summer Semester Example A circular loop of wire with radius r=5.0cm is in a magnetic field as shown. The Area vector of the loop is pointing in the x-direction. The magnetic field is: The magnetic field is turned off at a constant rate over a 5 second period. Calculate The induced emf in the loop. Voltmeter

Physics for Scientists and Engineers II, Summer Semester Example

Physics for Scientists and Engineers II, Summer Semester Example a b A loop of material in a magnetic field is turned over as shown. The turn takes 0.50 s. The resistance of the wire loop is 0.2 . Calculate the induced current during this event. Assume that the loop is turned over at constant angular speed. The loop has width a=2.0cm and height b=4.0cm. B=1.0T.

Physics for Scientists and Engineers II, Summer Semester Example

Physics for Scientists and Engineers II, Summer Semester Motional emf

Physics for Scientists and Engineers II, Summer Semester Motional emf R

Physics for Scientists and Engineers II, Summer Semester Motional emf R

Physics for Scientists and Engineers II, Summer Semester Motional emf

Physics for Scientists and Engineers II, Summer Semester Force required to pull the bar (no free lunch!) R

Physics for Scientists and Engineers II, Summer Semester Power comparison