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”

“Mediums” or Conductos

Wire Traces on a circuit board Air (lightning) Your body if you get electricuted

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 – 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: LED1 CQX35A

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)

R1 1k100

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:

Now for you…

Look under today’s date on the website and compete the 2 Activities!

Show me as you finish each one.