# Electricity

## What happens? ## How We Approach Electricity

• Electricity can be beautifully described with physics and mathematics
• However, we will focus on building an intuitive understanding and applying principles to build devices
• There will be some basic math, but that is not our focus
• Rules of Thumbs

## Electricity Analogies  ## Common Analogy

• Electricity can be thought of as water flowing down a pipe

• The higher the water falls from, the greater the pressure

• More water can flow (and flow faster) through a larger and smoother pipe

• If the water is stored in a container / vat, it will pour out until it is empty (like a battery)

## Common Analogy

• The “pressure” (or height) of the water is the voltage
• Measured in units called volts (V)
• Higher voltage means more potential energy
• Our circuits will typically consider voltages 0v - 5v

## Common Analogy

• The “rate of flow” of the electricity is the current
• Measured in units called amperes or amps (A)
• Higher amperage means electrons are flowing faster
• In equations, current with be denoted with the letter I
• Note: 1 A is a lot! Our projects will consider smaller values such as 0.2 A.
• Instead, we will say 0.2 A is 200 milliamps (mA)

## Compare Consider two equal water jugs connected to two different straws. Which has greater flow?

## Compare ## Resisting the Flow

• The narrower pipes restrict or resist the flow of water
• The measure of how well something resist or allows electricity is resistance
• Measured in units called Ohms (Ω)
• More Ohms means more resistance, which means less current (flow)

## Key Concepts

• Electrons are negatively-charged particles
• Electricity is the flow of electrons from positive to **negative **(flow of energy)
• Electronics is the study of devices that control / interact with the flow of electricity

## Circuits

• Electricity will only flow if there is a circuit
• A circuit is a complete loop from a positive voltage source to a negative (lesser) source, through a conductive material ## Voltage as Difference

• When we describe voltage, we are measuring the difference between two points
• In the water analogy, water could fall from 500 ft to 400 ft, or from 100 ft to 0 ft
• In both cases, water fell a difference of 100 ft, but the reference point changed
• In a circuit, we commonly call the reference point Ground (GND) and say it is 0V

• In homes and buildings, ground is literally connected to the earth

## Voltage Source

• In our circuits, we will use a voltage source to provide energy potential
• USB power: 5v (also stepped down to 3.3v which the Argon uses)
• 9V battery: 9v
• Rechargeable lithium battery: 3.7v
• Our circuits will have a positive voltage (e.g. 3.3v or 5v) and ground voltage (0v)
• We will consider that current flows from the positive part of the circuit to the negative

## Resistors

• Resistors conduct electricity, but are used to restrict / slow the flow of current
• They can be connected either direction
• We measure values from 0Ω to 10,000Ω
• 10,000 Ohms is 10 kiloOhms (10 KΩ)  ## Accessibility Note

• Resistor values are determined visually by color bands
• Unfortunately resistor labeling is not accessibly designed
• To support students who are color blind or have difficulty distinguishing colors, here are resources for support

## Ohm’s Law

• There are only a couple electrical laws that we need to know
• There is a relationship between voltage (V), current (I), and resistance (R)
``````V = I * R
R = V / I
I = R / V
``````
• If you know two, you can solve for the other one

## Example 1.) The voltage source is 9v. If we have a resistor that is 300 Ohms, what is the current? 2) The voltage source is 9v and you want to provide a current of 9mA. What size resistor should we use?

• We will use breadboards to connect our circuits
• The power rails (on the long ends of the board) are all connected together
• On the interior, each group of 5 pins are connected • Breadboards are built with rows and columns of connected pin sockets
• Underneath each row and column are strips of metal that form electrical connections    