Download EM Guided Notes KEY

Electromagnetism
Name:
When you walk across the carpet during the winter time and touch a door knob,
you often see a flash of light and hear a small pop. What causes that? It is due to a static
discharge. As you walk across the carpet, electrons are stripped by friction from the
carpet onto you. Like charges repel, so the electrons are trying to flee from each other.
When you approach the door knob, the electrons make the leap from you to the door
knob and a miniature lightning bolt forms.
Just like water flowing downhill, free electrons move from a position of high
potential energy to a position of low potential energy. When the charges are accelerated
(speeding up or slowing down), an electric flow is produced. That is electricity current.
Electricity and magnetism are closely related. A strong magnet is formed when
the domains in an object become aligned in the same direction. A magnet produces a
magnetic field, that is, a region where magnetic force is produced. The closer the
magnetic field lines, the stronger the force produced. The magnetic field lines of the
earth run from the north pole to the south pole and are closest together at the poles. That
means the magnetic field is strongest there.
Aligned domains are one way that magnets are formed. Another way to form a
magnet is by moving electric charges. Electric charges that are not moving do not form a
magnetic field, but when they go into motion, the magnetic field is formed. Hold a
compass next to an electric wire, and the needle will deflect if the current starts flowing.
An electromagnet is a magnet formed by current flowing through wire loops.
The strength of the magnet may be increased by increasing the current, the number of
loops, or by wrapping the loops around a piece of iron. One advantage to an
electromagnet over a permanent magnet is that the electromagnet can be turned on and
off.
This is how a stereo speaker works. The signal comes from the computer or CD
player. When the strength of the current increases, then the strength of the magnet
increases. That causes the speaker cone to move and recreates the sound of the music.
Another common tool that uses this concept is a credit card. The card has a
magnetic strip incorporated in it. If the strip is not moving, there is no current. But when
the strip moves through a reader, a particular current is formed which carries information
about the cardholder. That is how the store knows who to charge the purchase to.
Electromagnetic force is one of the four fundamental forces in the universe. The
E-M force is responsible for holding together all matter. Gravity is also an attractive
force that is well known. Lesser known are the other two forces. The nucleus is made of
protons and neutrons. But the protons all have a positive charge, which causes them to
repel. The strong nuclear force is stronger than the electromagnetic force pushing them
apart, so the nucleus stays together. The fourth force, the weak nuclear force, is
responsible for radioactive nuclear decay.