Download Electricity

Introduction to Electric Circuits
What is Electricity?
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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
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Wire
Traces on a circuit board
Air (lightning)
Your body if you get electricuted
AC/DC
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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
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Voltage (V)
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Current (I)
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Provides the “Push”
Measured in “Volts”
Flow of Electrons
Measured in Amperes (Electrons per second)
Resistance (R)
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Restricts the amount of current
Measured in Ohms (Ω)
Voltage
Measures the “imbalance of electric charge”
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a battery
Parallel Port on the computer
Power Supply box
Currant
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Sources of current are harder to describe
Think of current as electrons flowing through
a wire
Resistance
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Sources of Resistance:
Safe Current and Voltage Levels
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Voltage: 30V
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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
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All circuits need:
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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
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Series
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Only one path for the charge to flow
Parallel
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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
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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
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Our circuit diagrams will always:
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Contain a legend explaining any symbols
Have a title and your name
Circuit Components: LED
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Stands for Light Emitting Diode
Polarity is important!
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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
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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 1k
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
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Ground
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Ground is where the positive charge flows to.
Symbol:
Now for you…
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Look under today’s date on the website and
compete the 2 Activities!
Show me as you finish each one.