IN THIS PRESENTATION:
•
What is electricity?
•
The water analogy.
•
Voltage/Electric Potential
•
Current
•
Resistance
•
Ohm’s Law
•
Electrical Safety
•
Sources of electric potential (batteries, power supplies, Arduinos)
WHAT IS ELECTRICITY?
• There are small particles of “charge” called
“electrons.”
• Some elements can pass electrons (conductors) and
some cannot (insulators).
• When electrons move through a conductor, we call it
electricity.
WATER ANALOGY FOR ELECTRICITY
• When water flows through the plumbing in your house,
there are three important things: the water pressure,
the rate of flow, and the amount of constrictions in the
pipes.
• Water pressure = Electric potential or “voltage.”
• Water current = Electric current or “amperage”
• Constrictions in the pipe = Electrical “resistance”
ELECTRIC POTENTIAL (VOLTAGE)
• Defined as the amount of potential energy in
the circuit.
• Symbol: V
• Units: Volts, or just V for short
Water
Tower
Water
Tower
V1
V2
ELECTRIC CURRENT (AMPERAGE)
• Defined as the amount of charge that moves
through a circuit in a given amount of time.
• Symbol: I
(Capital ‘i’ because of the French word for ‘intensity’)
• Units: Amps, or just A for short
CURRENT FLOW ANALOGY
High Current
Low Current
RESISTANCE (IMPEDANCE)
• Like it sounds, this describes how much
something resists the flow of current.
• Symbol: R
• Units: Ohms, or just Ω for short (the Greek letter ‘omega’)
RESISTANCE ANALOGY
Water
Tower
Water
Tower
V
V
Big Pipe == Lower Resistance
Small Pipe == Higher Resistance
OHM’S LAW
This law describes the relationship between the voltage (V), current (I), and resistance
(R) of a circuit.
Here it is in three algebraically equivalent forms:
SAFETY: DAMAGE TO OUR RESOURCES
Damage to electrical systems:
•
Overload: too much voltage/current and not enough resistance. Can result when
there is a “surge” or electricity. Hence, surge protectors.
•
Short circuit: when there is too little resistance in a circuit. Often the accidental
result of insufficient or faulty insulation around conductors.
Preventing overloads and short circuits:
•
Use Ohm’s Law to predict the proper values of V, I, and/or R for your circuit before
you connect and real power supply.
•
Use insulated wires and components and inspect them for damage before use.
SAFETY: DAMAGE TO YOU! ELECTRICAL SHOCK
Important factors:
• Frequency of current:
• AC (wall outlet) is much more dangerous than DC (batteries)
• Amplitude of the current:
• You can stop your hear with 300-500 mA of DC current, or only
30 mA of AC current!
• Path through body:
• Across your heart and lungs is the worst.
SAFETY
Preventing electrical shock:
•
Never work on something that is currently plugged into a wall outlet or that will be
plugged in in the future.
•
Remove batteries from objects when working on them.
•
Do not work with 12V lamp batteries, car batteries, power drill batteries, laptop
batteries, or anything similar.
•
Always use insulated wires.
•
Carefully inspect circuits before you power them.
•
Be careful of close connections (i.e. solder points on a circuit board)
SOURCES OF ELECTRIC POTENTIAL
Batteries
• Labeled with their voltage.
• Connecting in series will add voltages together.
• Expensive and environmentally taxing.
• Safer than anything plugged into a wall outlet.
• Power Supplies
• Turns alternating current, high voltage electricity from the wall outlet into manageable
direct current.
• Adjustable voltage and current.
• Expensive if damaged.
• Potentially dangerous (connected to wall outlet), but have protective fuses.
• Arduinos (when powered)
• Have a regulated 5V and 3.3V output.
• Limited amount of current can be supplied.
• Ardunios can potentially be damaged ($$$).
•