This lesson goes over the fundamentals of electronics from current, resistance, voltage, and how to use schematics to understand electronic circuits.

Electricity and Electronics

A group of three circuit schematics. Circuit one has a voltage source of unknown value, a current value of 0.5 amps, and a resistor value of 10 ohms. Circuit two has a voltage source value of 24 volts, a current of unknown value, and a resistor value of 120 ohms. Circuit three has a voltage source value of 3.3 volts, a current value of 0.02 amps, and a resistor of unknown value.

Electronic circuits involve the manipulation of voltages, currents, and resistances. Knowing how these three properties relate to each other is a foundational part of circuit design. These relationships are described using the equation, **Ohm's Law**. 

The formula of Ohm's Law is as follows:


```tex
V = I × R
```

Where:
- V = voltage expressed in Volts
- I = current expressed in Amps
- R = resistance expressed in Ohms

_Note: Voltage is sometimes represented in Ohm's Law using "E"_

If two values are known, we can use algebra to reconfigure Ohm's Law and calculate the third value:

To find the current, divide voltage by resistance.
```tex
I = V ÷ R
```

To find resistance, divide voltage by current.
```tex
R = V ÷ I
```
![Schematic diagram with a voltage source and a resistor. The voltage of the voltage source is represented by V, the current through the loop is represented by I and the resistance of the resistor is represented by R](https://static-assets.codecademy.com/Courses/learn-raspberry-pi/elec_schematic_ol_e6.png)

The above schematic has a voltage source with an unknown voltage. There is a current, **I = 2A** through a load resistor, **R = 4.5Ω**.  Using Ohm's Law we can find the voltage of the circuit's voltage source:

```tex
V = I × R
```
```tex
V = 2A × 4.5Ω
```
```tex
V = 9V
```

The above example contains one voltage source and one load resistor. In general, a circuit's load will consist of multiple components. In this case, you will need to find out how much of the source voltage is used by each component when applying Ohm's Law. 

Ohm's Law

We now understand that the driving force within a circuit is voltage, and the flow of electrons through a circuit is current. We will now look at the opposition of current within a circuit known as **resistance**.

Resistance opposes the flow of electricity and is measured in ohms, symbolized by the Greek letter omega (Ω). 

Using the water analogy one last time we can represent resistance by the diameter of the water pipe. A thinner pipe will slow the flow of water through the entire length of the pipe, not just the thinner portion.

![Resistance analogy with water flow that is slower because of a change in the pipe diameter.](https://static-assets.codecademy.com/Courses/learn-raspberry-pi/elex_resistance_analogy_s.png)

The decrease in the pipe diameter is the circuit equivalent of an increase in resistance or opposition to current flow. Controlling the resistance of a circuit is used to protect components by controlling the amount of current and voltage in a circuit.

One of the most common components in electronic schematics is the resistor.

![A resistor schematic symbol consists of zig zag line between two straight lines for terminals.](https://static-assets.codecademy.com/Courses/learn-raspberry-pi/elec_resistor_e5.png)

Resistors are used in circuits to limit current or to achieve a specific voltage for another component. 

Resistors are commonly used in circuit schematics on their own to study how they affect the voltage and current within a circuit.

Resistance is in all conductive paths. If you have ever felt the cord of a large appliance, it can get hot. This heat is caused by the resistance in the conductors of the cord!

Resistance

When we talk about the flow of electricity, we are specifically referring to **current**. 

Current is the rate at which electrons flow through a circuit. With a voltage applied to a circuit, the current will flow through the conductive loop and load. We can measure current in units of Amperes or amps (A).

Current also comes in two forms, Direct Current (DC) and Alternating Current (AC). Direct current refers to the flow of electricity in one direction. Alternating Current is the flow of electricity that periodically reverses direction. In this lesson, we will cover direct current.

If we go back to the water analogy and look at electricity as a water tank with a pipe attached below it, we can think of current as the flow of water through the pipe.

![Current analogy of a water tank with pressure that creates water flow through a pipe.](https://static-assets.codecademy.com/Courses/learn-raspberry-pi/elex_current_analogy_sm.png)

Many things can affect the flow, such as the water pressure (voltage). A higher volume of water will increase the pressure (voltage) in the tank and result in an increase in flow (current) through the pipe.

With all elements in a circuit staying the same, a higher voltage will result in a higher current will flow, while a lower voltage will result in less current. 

A simple way to control the current in a circuit is a push button.

![Push button schematic that represents an open conductive path.](https://static-assets.codecademy.com/Courses/learn-raspberry-pi/elec_button_op_e4.png)

The schematic has 2 lines with circles at the ends which represent the conductive path. When the top portion of the schematic is not touching the circles, the circuit is open and there is no current. 

When the top pad is touching the circles, the circuit is closed and there is current. The closed-circuit button is represented by the schematic below.

![Push button schematic that represents a closed conductive path.](https://static-assets.codecademy.com/Courses/learn-raspberry-pi/elec_button_cl_e4.png)

Current

Circuit schematic with a voltage source, push-button, resistor, and light-emitting diode.

Awesome work! We've covered a lot regarding electricity and electronics! Let's recap what we've learned so far:

- Electronic circuits consist of 3 basic elements: An electric source, a load, and a conductive path
- Voltage is measured in volts (V) and is defined as the amount of electric potential energy between two points
- Current is measured in amps (A) and it's the measurement of the flow of electricity through a circuit
- Resistance is measured in ohms (Ω) and is the measure of the opposition to current flow in an electric circuit
- Schematics are diagrams used to represent a circuit. 
- Some schematic symbols include, a voltage source, push-button, resistor, and an LED
- Ohm's Law, V = I × R, is a fundamental rule of electronics that represents the relationship between voltage, current, and resistance
- LEDs are used as circuit indicators and allow current to only flow in one direction
- Forward voltage is the recommended voltage to be applied by an LED with a resulting current known as the forward current

With this knowledge, you will be able to build up a better understanding of more complex concepts that have to do with electric circuits and electronics in general.

Congratulations on completing this lesson!



Conclusion

Circuit schematic with a voltage source of 5 volts, a resistor of unknown value, and an LED with a forward voltage of 2 volts and a forward current of 0.03 amps.

In a previous exercise, we applied Ohm's law using a circuit with a single resistor as the load. In this lesson, we will look at a load that consists of two components: a resistor and an LED.

![Circuit schematic with a voltage source of 9 volts, a resistor of unknown value, and an LED with a forward voltage of 1.4 volts and a forward current of 0.02 amps.](https://static-assets.codecademy.com/Courses/learn-raspberry-pi/elec_schematic_rl_e8.png)

The circuit above has an LED with a forward voltage (Vf) of 1.4V which is smaller than the source voltage (V) of 9V. To address this difference in voltage, a resistor is placed in the circuit to share some of the applied voltage. 

The goal now is to find the value of the resistor that will share the right amount of voltage and induce the necessary current.

Before we get into the math, we first need to cover two rules of this circuit:
- **Rule 1:** The sum of the voltages in the load will equal the voltage source. In the example circuit, the voltage across the resistor (Vr) added to the forward voltage (Vf) of the LED will equal 9V.
- **Rule 2:** The current through all the components will be equal. Remembering the resistance water analogy, the smaller portion of the pipe will dictate the water flow for the entire pipe. In the example circuit, the resistor will dictate the goal current which is equal to the forward current of the LED, 0.02A.

Now let's plug in the numbers using rule 1: The sum of the voltages in the load will equal the voltage source
```tex
V = V_{r} + V_{f}
```
```tex
9V = V_{r} + 1.4V
```
```tex
V_{r} = 9V - 1.4V
```
```tex
V_{r} = 7.6V
```
Using this answer from the previous equation and circuit rule 2 we now have enough information to apply Ohm's Law:
1. The voltage across the resistor is 7.6V
2. The goal current through the circuit is equal to the LED forward current, 0.02A 
```tex
R = V_{r} ÷ I
```
```tex
R = 7.6V ÷ 0.02A
```
```tex
R = 380Ω
```
Picking a resistor to go along with an LED is an important multi-step task. Move on to the instructions to give it a try on a new circuit.

Creating an LED circuit

Before diving into building electric circuits, lighting up LEDs, and creating food-serving robots, we must first understand the basics. So, what exactly is electricity? 

Electricity is the flow of electrical charge and is one of the most widely used forms of energy. When we talk about "electronics", we're essentially manipulating electricity to accomplish a particular task. 

Electronic circuits like the one displayed on the right are often vast arrays of components and conductors, but they are all made up of much smaller and less complicated pieces. Once you appreciate some of these smaller circuits, you can move on to working with more advanced circuits. 

In this lesson, we'll take a look at:

- How to define an electronic circuit
- Understand the electrical properties, **voltage**, **current**, and **resistance** and how they relate to each other
- Explore **Ohm's Law** and its usage
- Explore **schematic** diagrams and their components

So without further delay, let's get started!


Introduction

**Light-Emitting Diodes** are circuit components that turn electricity into light. They are a type of diode, which is a circuit component that only lets current flow in one direction.

Also known as **LEDs**, light-emitting diodes are used as circuit indicators to let us know if something is powered on or maybe if something is wrong. When grouped together LEDs can be used to display images, like in computer monitors and TVs.

![Light-Emitting Diode schematic symbol](https://static-assets.codecademy.com/Courses/learn-raspberry-pi/elec_led_e7.png)

The schematic symbol for an LED is a triangle with arrows coming off of it pointing toward a line. The arrows represent the light-emitting behavior of the component. 

The triangle pointing to the line represents the direction the current will flow. Current flows into the LED from the positive terminal and exits the negative terminal.

When including LEDs in a circuit we must provide it with a specific voltage and current. These two attributes are known as **forward voltage** and **forward current**.

##### Forward Voltage (Vf)
An LED is a load that requires voltage provided by the voltage source. In most cases, the LED can not have the entire source voltage applied to it or it will be damaged. 

Forward voltage, represented by Vf, is the optimum voltage that should be applied to an LED. Going under this voltage by too much will result in reduced current and poor illumination (or none at all). Going over the forward voltage by too much will damage the LED.

##### Forward Current (If)
When the forward voltage is met, the current that goes through the LED is known as the forward current, represented by If. This value is used to help design the circuit for optimum LED operation.

Light-Emitting Diodes

**Voltage** is the amount of electrical potential energy between two points. It's measured in Volts and represents the force that sends the electrons through a circuit's conductive path and load.

We can think of voltage as "pressure". This pressure comes from a power source (i.e. a battery) and pushes electrons through the conductive path. Voltage is measured **across** two points and will only cause electricity to flow if there is a conductive path between those 2 points.

Consider a water tank with a pipe attached below it where water can pass through it. We can use this analogy to represent voltage as the pressure of the water in the tank.

The greater the amount of water in the tank, the greater the pressure at the bottom of the tank. 

![Voltage analogy of a water tank that applies pressure to the bottom of the tank](https://static-assets.codecademy.com/Courses/learn-raspberry-pi/elex_voltage_analogy_sm.png)

Now imagine there was no pipe attached to the tank and the water has no place to go. There is still pressure at the bottom of the tank. This is the same in circuits. A battery on its own has a voltage, but electricity won't flow until it is connected to a conductive path and a load.

Below is the schematic representation of a voltage source, usually representing a battery.

![A schematic symbol of a battery consists of a group of alternating short and long horizontal lines.](https://static-assets.codecademy.com/Courses/learn-raspberry-pi/elec_battery_e3.png)

In this lesson, we will work with voltage sources like the schematic above. They will have a positive terminal (the top vertical line) and a negative terminal (the bottom vertical line). When a voltage source is attached to a circuit it is a convention that electricity flows out of the positive terminal, through the conductive path and load, and back into the negative terminal.


Voltage

A circuit diagram with three components connected by conductive paths.

An electronic circuit is a path for transmitting electric current supplied by an electric source. In order for a path to be a circuit, it must start and end at the source. 

The very name "circuit" implies that the structure is closed and oftentimes we represent these circuits as loops. However, when using elements like switches, the circuit is then called "open" since the connection is incomplete.  

A closed-circuit is a loop that allows the flow of electricity, while an open circuit stops the flow with a break in the circuit, such as a room's light switch.

There are many different types of components that can be involved in circuits, however, all circuits are made up of three basic elements:

- Electric source: A source of electricity, which can come from a two-terminal device such as a battery. The source can be any component that provides a potential difference (voltage) between two points in the circuit.

- Load: A circuit element, or elements, that consume power and use electricity in order to perform a function. A light bulb is a common example, but loads can come in many forms such as LEDs, motors, or circuit components we call resisters. 

- Conductive Path: This is the path through which the energy is able to flow, usually made of a metal like copper or aluminum. It begins from the voltage source, travels through the load, and finally returns to the voltage source