Class Copy

# Electromagnetic Force

There are four force fields in nature: strong atomic force, weak atomic force, electromagnetic force and gravity. That is it, just four - forget all the sci-fi stuff.

## The Electromagnetic Force

1. Acts on charged particles in an electromagnetic (EM) field.
2. The EM field has both an electric and magnetic field.
3. A changing electric field produces a magnetic field. ∗
4. A changing magnetic field creates an electric field. ∗
• ∗ This is important! This allows us to have electric generators, motors and transformers. No, not that kind of Transformers ®.

## Manifestations

1. Electromagnets - An electric current moving in a wire generates a magnetic field. We often coil the wire to increase the strength of the magnetic field.
2. Permanent magnets - A magnetic force field can be generated by the arrangements of a particle's electrons. Iron, nickel and cobalt are common magnetic materials.
1. A compass has a magnetized needle that is free to move. The Earth's core produces a magnetic field. The compass's magnet interacts with the Earth's magnetic field. Note the Earth's geographic north pole is the Earth's magnetic south pole! Magnetic fields are 3-D; what does mean when you are using a compass near the poles?
3. Motors use either electromagnets or permanent magnets to create a magnetic field. Electricity following in coils of wires generates an opposing magnetic field. The feuding fields cause the motor rotor to spin.
4. Generators use either electromagnets or permanent magnets to create a magnetic field. Spinning the wire coils attached to the generator's rotor causes electricity to flow.

## Useful Parts

1. Wires are made of metals such as copper. Metallic elements have electrons that are not held close to the element's atoms. It is as if there was a cloud of electrons around the atoms. This allows the electrons to move easily and thus the metal conducts electricity. Insulators do not have these highly mobile electrons and so do not conduct - they stop the flow of electricity.
2. Lamps are a wire in a vacuum or inert gas enclosed by a glass envelope. The wire material, typically tungsten , gets white hot when enough electricity flows through it. The electricity may flow either direction through the lamp. The lamp is pretty tough - it can handle small amounts of too much voltage. Note: a light emitting diode (LED ) is a completely different technology. Electricity can only flow one direction in an LED. Reverse connections or too much voltage will destroy it instantly.
3. A cell is a device that derives electrical energy from chemical reactions. There are several different chemistries possible depending on the amount of electricity needed and the costs. More than one cell connected together is called a battery . A rechargeable cell has a reaction that can run backwards by adding electricity!