MOD 4  LECTURE 2                                           ELECTRICITY BASICS

In this lecture you will learn:

Electromagnetism is one big section of physics that explains the rules of the movement of energy through matter.  For the most part "matter" means how electrons react to changes in energy levels. 
If you click on the picture on the right it will take you to the website of hyperphysics where you can slake any thirst for physics, and now they have sections on chemistry, geophysics and biology. 

Most science courses start with mechanics (the rules that govern the movement of matter through space) because scientific physics for the most part started with experimentation in the movement of matter; the planets around the sun and how to get a heavy ball to hit the side of a castle wall, or, how to get an arrow into a target. 

This course starts with atoms (matter), moves to types of energy, and then on to the interactions of energy and matter. First the interaction of energy with electrons, and later the energy of the movement of mass itself (mechanics) although only a small portion of it - kinetics. 

"Electromagnetism is the physics of the electromagnetic field, a field which exerts a force on particles with the property of electric charge and which is reciprocally affected by the presence and motion of such particles.

A changing magnetic field produces an electric field (this is the phenomenon of electromagnetic induction, the basis of operation for electrical generators, induction motors, and transformers). Similarly, a changing electric field generates a magnetic field.

The magnetic field is produced by the motion of electric charges, i.e., electric current. The magnetic field causes the magnetic force associated with magnets."  cite: wikipedia


 
VOCABULARY
VOLTAGE

is the measure of the POTENTIAL ENERGY of a charge

It is measured between the ELECTRICAL source and the GROUND

the HIGHER the potential, the HIGHER the voltage

- Imagine water behind a dam. If there is a 1 foot drop over the dam, it is nice, but if this dam bursts, there is little more than a ripple.

-----  There is LITTLE POTENTIAL OR VOLTAGE behind the dam because there is only a SMALL DROP.

- If there is a 25 foot drop, there is a LARGE potential difference so if this dam bursts, there is tremendous energy released. THERE IS HIGH POTENTIAL OR HIGH VOLTAGE behind this dam.

The size of the flow of electrical charge depends (of course) on how big the potential difference is.  There isnt  going to be a big flow if there isnt a big dam holding back a lot of water.


CURRENT

- is the flow of an electrical charge through a CONDUCTING material.

current WILL NOT flow unless it flows toward a ground

IF IT DOESNT HAVE ANYWHERE TO GO, IT WONT FLOW

AMPERAGE (amp)

is the measurement of how much electrical charge moves pass a point per second
current is the movement, amperage says how much/how fast

-- the size of the flow DEPENDS on:
1. the voltage (potential)
2. the size and resistance of the conductor or wire

low voltage cannot provide much electricity (why low volt lights are used outside where even if they get wet they wont electrocute anybody)

-- think of the size of the conductor as the difference between a trickle of water coming out of a faucet or garden hose and the torrent of water of a white water river.  Which would you stand in front of?

so thin, fine, low amperage wires cannot carry much electrical charge before they heat up and melt down. (This is the basis of the old fashioned fuse. A thin wire inside a glass tube.)
 
 

- A thick wire, like those used for lightning rods, can carry a huge load of amperage without melting down.

it is VERY important that the electrical cord is matched to the amperage drawn by any device.  A cheap, thin extension cord will quickly overheat, melt down, and start a fire

VOLTAGE AND AMPERAGE

- Let's say that you are standing at the bottom of Hoover Dam. You are perfectly safe if there is no pathway connecting where you are and where the water is above you. If, however, there is a conduit, you are still safe as long as the conduit is a low amperage "faucet ". 

If, however, someone opens a gate to a huge conduit (a high amperage faucet), run.

RESISTANCE
See Resistance at the Molecular Level here

- anything that opposes or reduces electrical current.
- Back to Hoover Dam. There is a huge conduit. But when you look inside, the entire conduit is filled with sand. As the water enters at the top, it can only leak through the sand. The sand resists the flow of the water. The water is constantly bouncing off of the grains of sand and this slows the water down. Resistance is measured in OHMS.
- all materials have some degree of resistance to the flow of electrical charges. Metals like copper offer little resistance. Glass or plastic are both non-conductors or insulators and offer a great deal of resistance to the flow of electrical charge. This is why wire is wrapped in plastic to insulate the wire and keep the charge inside from leaking out and grounding to anything it touches.

Resistance produces heat. Tungsten has high resistance.  It heats so much it glows and the excited electrons give off energy in the visible spectrum. Incandescent lights give off both visible light and infrared. We cannot see IR so it is "wasted" energy compared with "cool" lights. 

OTOH, electrical heating devices use the same idea but dont waste energy in the visible spectrum.  Those red "heat lights" seen in stores produce some red light to (I guess) reassure consumers they have a heat lamp.  

WATT

- the flow of the electrical charge can be tapped to DO THINGS.

- water in a river is current. But to make it DO SOMETHING, the flow of water is used to turn paddle wheels. This can be hooked up by a belt to turn a wheel that grinds wheat for example. Or turn the blades of a fan.

- WATT is a measurement of the CONVERSION of electrical energy into SOME OTHER FORM OVER TIME (PER SECOND).

FOR EXAMPLE:
A 100 Watt incandescent light bulb converts 100 Joules of electricity per second into light and heat. A 100 Watt fluorescent light bulb converts the same amount, but mostly into light which means it is brighter since little of the joules are wasted as heat.

REVIEW QUESTIONS:
Voltage
current
Amperage
Resistance
Watt
How is voltage related to amperage?
How is amperage affected by resistance?
Why are low voltage lights safe?
Why are thin wire extension cords not used for high amperage electrical devices?
what is the difference between a 100 watt incandescent light and a 100 watt  fluorescent light?