SAMI

MAKERSPACE

M A K E : AN E

L E C T R O N I CS W

O R K S H O P

ELECTRICITY

BASICS

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

ELECTRICIT

Y?

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

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

POTENTIA

L

(VOLTAGE)

ELECTRIC POTENTIAL (VOLTAGE)• Defined as the amount of

potential energy in the circuit.

• Symbol: V

• Units: Volts, or just V for short

WaterTower

WaterTower

V2V1

ELECTR

IC

CURRENT

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

RESISTAN

CE

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

Big Pipe == Lower Resistance Small Pipe == Higher Resistance

WaterTower

WaterTower

VV

OHM’S

LAW

OHM’S LAWThis law describes the relationship between the voltage (V),

current (I), and resistance (R) of a circuit.

Here it is in three algebraically equivalent forms:

ELECTRICA

L SAFETY

SAFETY: DAMAGE TO OUR RESOURCESDamage 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.

SAFETYPreventing 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

POTENTIA

L

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 ($$$).