Introduction to Electric Circuits

What is Electricity? No one really knows… A good definition for our class is: “Electricity is the flow of electrons along a medium. This flow is caused by an imbalance of Electric Charges”

AC/DC All household electricity is Alternating Current, this means the electrons in a wire vibrate back and forth to produce power All of our circuits will use Direct Current which means the electrons will flow from negative to positive along a closed circuit.

Three Invisible Quantities Voltage (V) Provides the “Push” Measured in “Volts” Current (I) Flow of Electrons Measured in Amperes (Electrons per second) Resistance (R) Restricts the amount of current Measured in Ohms (Ω)

Voltage Measures the “imbalance of electric charge” a battery Parallel Port on the computer Power Supply box

Currant Sources of current are harder to describe Think of current as electrons flowing through a wire

Resistance Sources of Resistance:

Safe Current and Voltage Levels Voltage: 30V Voltages inside a computer do not exceed 12 V, except at the power supply and power switch on older computers, which are at 120 V. Be careful in these areas! Current: 5 mA (0.005 Amperes)

Water Analogy Think of Electricity as river: Voltage is the slope of the river. Current is the volume of water flowing Resistance is stuff like beaver dams and sunken boats that allow less water to get through.

Electric Circuits All circuits need: A Medium (wire, Vacuum tube, your body…) An applied voltage (Battery, power supply) Current flows from positive to negative when there is a closed loop Note: It is actually the electrons that are flowing from negative to positive, but for sake of tradition and convention we say the positive charge flows from positive to negative. (Protons don’t move!)

Two Types of Circuits Series Parallel Only one path for the charge to flow Parallel More then one path

A Circuit In Series Only one path for the electrons to flow

A Circuit in Parallel More then 1 path for the electrons:

A Short Circuit Electricity always follows the path of least resistance to get from the power to the ground. When it takes a short cut it’s called a “Short Circuit”

Circuit Diagrams Our circuit diagrams will always: Contain a legend explaining any symbols Have a title and your name

Circuit Components: LED Stands for Light Emitting Diode Polarity is important! Short lead goes to ground The flat side of the LED goes to ground “The line, is the line, is the line” Schematic Symbol:

Resistors Resistors are used to “limit current” and drop voltage. (Remember Ohm’s law?) The schematic symbol is: Always label resistors with the resistance value (in Ohms) 100

Resistor Colour Chart

Reading Resistor Values Start at the end opposite the gold or silver band Write down the first two numbers The last numbers tells you how many 0’s Ex: Red – Brown – Orange = 2 - 1 - 3 The resistance is 21000

Ground Ground is where the positive charge flows to. Symbol: