ELECTRICITY FUNDAMENTALS

Relevant Reading in the Book:

Electricity is an apparent force in nature that exists whenever there is a net electrical charge between any two objects.

Basics of Electrostatics:

Properties of Electricity:

What Stan Said: (we will be going over this stuff in other lectures as well).

Energy has different forms:

Energy is always conserved:

Energy is neither created or destroyed it can only be converted from one form to another.

Units of Energy:

Energy has units of mass x (length/time)2 This is called a JOULE.

Power:

Power is the rate of energy usage or:

Power = Energy/Time
Energy = Power x Time

The basic unit of power is a Watt. 1 Watt = 1 Joule/Sec.

1 Watt-second = 1 Joule.

3600 Watt-seconds = 1 Watt-hour = 3600 Joules

1000 Watt-hours = 1 Kilowatt hour (KWH); A KWH will be our basic unit of energy in this class. You purchase KWHs from the electric utility whenever you use power in your home.

Forces:

Electro-magnetic Force:

This force is similar to gravity in some respects except that it is both a repulsive and attractive force. Electricity is a result of the application of electro-magnetic force to objects.

The basic carrier of electric charge in an atom is the electron. The units of charge are denoted as q, which is the charge of an individual electron.

On standard unit for charge is the Coulomb but this represents a very large charge. 1 Coulomb represents about 6 x 1019 individual electrons!

Conservation of Charge:

This is similar to conservation of energy. Charge can neither be created or destroyed but just transferred.

When you rub a rod on a wool cloth to create 'static" electricity - you are not creating charge. Your are merely transferring electrons from one object to another to produce a charge imbalance.

Voltage:

Imagine that you have two opposite charges that you want to separate. It takes work to separate the charge and thus the separated charges store energy. The amount of stored energy is given by:

E = qV where V is the voltage or electric potential of some system.

The units of voltage or Volts: 1 Volt = 1 Joule/Coulomb

If the separated charges get back together, work/energy can be extracted from the system. If there is some pathway for the charges to flow then we get a current. Current is denoted by I and is in units of amperes or amps 1 Ampere = 1 coulomb/second

What do you get if you multiply Voltage by Current?

Joule/coulomb x coulomb/second = Joule/second = Power

Power = V x I

the voltage in your house is 120 Volts (that's a standard in America). If you have a 100 Watt light bulb it will draw 100/120 = .83 amps of electricity.

If you leave this 100 watt light bulb on for 10 hours you have used 1 KWH hour of electricity. Alternatively you have used 8.3 amp-hours of electrons. Your utility company had to sell you this many electrons to kepp your bulb lit for 10 hours and that's what you paid for.

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