Introduction to Physical Science

Monday, Wednesday, Thursday

Tom Burbinetomburbine@astro.umass.edu

Magnetic Poles

• Like poles repel

• Opposite poles attract

• North pole

• South pole

Magnetic Force

• 1) Between magnets, it is the attraction of unlike magnetic poles and the repulsion of like magnetic poles

• 2) Between a magnetic field and moving charge, it is the deflecting force due to the motion of the charge

Difference between magnetic poles and electron charges

• Electric charges can be isolated– Protons and electrons can exist separately

• Magnetic poles cannot– North magnetic poles can’t exist without south poles

• If you break a magnet in half, each half will act as a magnet

• If you break that piece in half, you will then have four magnets

• This suggests that the atoms themselves are magnets

Magnetic Field

• The region of magnetic influence around a magnetic pole or a moving charged particle

• Field of force

Motion of electric charges

• Electron spinning

• Electron revolution around the protons

Electron spinning• An electron spinning creates a magnetic field

• A pair of electrons spinning in the same direction creates a stronger magnet

• A pair of electrons spinning in the opposite direction work against each other

Metals• Materials such as iron, nickel, and cobalt have

electrons whose spins do not cancel out

• Iron has four paired electrons that can have the same spin

Magnetic domains

• Clusters of atoms line up with one another

Permanent Magnet

• Place a piece of iron (or a similarly magnetized material) in a strong magnetic field

• Moving charge produces a magnetic field

• A current of charge produces a magnetic field

Electromagnetic Induction

• Electric current can be produced in a wire simply by moving a magnet into or out of a coil of wire

• A voltage is induced by the relative motion between a wire and the magnetic field

Faraday’s Law

• The induced voltage of a coil is proportional to the number of loops multiplied by the rate at which the magnetic field changes within those loops

• More practical to move the coil then move the magnet

• Generator has a rotating coil in a stationary magnetic field

• Converts mechanical energy into electrical energy

• http://video.google.com/videoplay?docid=3902466783636795302#

Any Questions?