Electrical Quantities and Units

In the metric system lecture we talked about Quantities as being properties that can be measured, for example, distance or volume. Every quantity has its own Unit, which represents the value of the quantity. For distance we used the meter as a unit and for volume we used the liter as a unit.

Now we need to take the metric system and apply it to the properties of the electrical field. Before we can work with electricity we need to have a grasp of the quantities and units that describe it. In this section we will go through quantities, symbols, definitions, units, and relationships. In class we form flash cards to study and memorize these terms. Please study your flash cards.

Charge - Q

Charge is a property possessed by both electrons and protons. Electrons have a negative charge and protons have a positive charge. The symbol for Charge is Q.

Coulomb - C

The Coulomb is the unit for charge. The symbol for the Coulomb is C

Proper usage:

Charge = 50C

Q = 50C

Current - I

Current is the flow of charge in a specified direction. The symbol for Current is I

Ampere - A

The Ampere or Amp is the unit for Current. The symbol for Amp is A

Proper Usage:

Current = 20 amps

I = 20A

An Amp is equal to a Coulomb per Second

Voltage - E

  1. Voltage is the electric force or pressure that causes current to flow.

  2. Voltage is the potential difference between two points of a circuit.

  3. Voltage is also know as electromotive force (EMF)

The symbol for Voltage is E (note that V is also used for voltage)

Volt - V

The Volt is the base unit for Voltage. The symbol for the Volt is V

Proper USage:

Voltage = 120 volts

E = 120V

A volt is equal to a Joule per Coulomb

REsistance - R

Resistance is the opposition to current flow. The symbol for Resistance is R

Ohm - Ω

The Ohm is the base unit for Resistance. The symbol for the Ohm is Ω (omega)

4 factors of Resistance

  1. Material

  2. Temperature

  3. Cross-Sectional Area

  4. Length

Proper Usage:

Resistance = 4700 ohms

R = 4.7kΩ

An Ohm is equal to a Volt per Amp

Power - P

Power is the rate of energy being used/converted in an electrical circuit.

Watt - W

The Watt is the base unit for Power. The symbol for the Watt is W

Proper Usage:

Power = 400 watts

P = 400W

A Watt is equal to Joule per Second