ELECTRICITY FUNDAMENTALS

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

Basics of Electrostatics:

• Electrical charges are either negative (electrons) or positive (protons)
• The unit of charge, q , is called the coulomb.
• When there are equal numbers of positive and negative charges there is no electrical force as there is no net charge. This is the case for a neutral atom.
• Electrical force is created when electrons are transferred from one material to another (e.g. rubbing a wool cloth with a plastic comb).
• Electrical charge is conserved; charge is neither created nor destroyed

Properties of Electricity:

CURRENT: denoted by I and measured in amperes. Current flows from negative material to positive material and is essentially the number of electrons per second that are carried through a conductor.

VOLTAGE: Potential difference between a negatively charged object and a positively charged one (like two terminals on a battery). Potential difference is measured in units of Volts ( V )which represents the work done per unit charge to move electrons between the positive and negative terminals. If a potential difference exists, then energy can be extracted.

RESISTANCE: Property of material that helps prevent the flow of electrons in it. Metals are good conductors due to low resistance. Wood is a poor conductor due to high resistance. Resistance, R , is measured in ohms and depends upon both the type of material and its size. Long wires have more resistance than short wires; thin wires have more resistance than thick wires. R is also temperature dependent.

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 keep your bulb lit for 10 hours and that's what you paid for.