Electricity

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

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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
Water can be stored in a container (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 straws. Which has greater flow?

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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)

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

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 Photon 2 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

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   
or Voltage = Current * Resistance

Rule of thumb: As resistance increases, the current decreases

Example

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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?

Building our Circuits on Breadboard

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

Inside a Breadboard

Breadboards are built with rows and columns of connected pin sockets
Underneath each row and column are strips of metal that form electrical connections