In this video, electrical engineer Barron Stone dives into the difference between alternating current (AC) and direct current (DC). Barron relates the concepts of how alternating and direct current perform work in an electronic circuit to how the teeth on
- [Instructor] There are two types of electricity that are commonly used to power electronic devices: direct current and alternating current. Direct current, which is abbreviated as DC, is current that always flows in the same direction through a circuit. Batteries are a common source of direct current because they produce a constant voltage, which pushes electrons around a circuit in one direction. For example, in this circuit consisting of a battery and a light bulb, the current will always flow from the positive terminal of the battery, to the negative terminal.
And as those flowing electrons pass through the light bulb, their electrical energy is converted into heat and light. And circuits that use alternating current, which is abbreviated as AC, the current is constantly changing direction at a regular interval. While outlets are a common source of alternating current, the voltage between the two terminals of a power outlet is not constant. Instead, one of the terminals is constantly switching between having a positive or negative voltage, relative to the other terminal, at a rate of about 60 times per second.
If I plug a lamp into the outlet, as the voltage changes it's orientation, it'll push electrons through the light bulb in alternating directions. With alternating current, the electrons are not making full laps around the circuit, instead they're just shifting back and forth in the same relative positions. Every time the electrons near the light bulb pass through it, their electrical energy is converted into heat and light to power the light bulb. To conceptualize the difference between direct current and alternating current, and to understand how they can both do work, I like to relate the electrons flowing through a light bulb to illuminate it, to the teeth of a saw blade that I can use to cut this board.
When I use direct current, it's like I'm using a chainsaw. The teeth of this chainsaw always travel in the same direction. They go around in a loop, and every time the teeth pass by the board, they do a little bit of work to help cut it. Using alternating current, is like using a good old-fashioned handsaw. When I push and pull the saw, I'm applying a force on it, like voltage, to move those saw teeth back and forth.
Every time the teeth move past the board in either direction, they do a little bit of work to cut it. Just like how each of the electrons moving back and forth in alternating current help to turn on the light bulb. In electronic schematics, the symbol shown on the left is used to represent sources of direct current, with the plus and minus symbols indicating that the voltage is always higher on one side then the other. The symbol shown on the right represents sources of alternating current, with the squiggly line indicating that the voltage will alternate back and forth, constantly changing directions.
In schematics, the voltage is usually written next to the source. And the abbreviations VDC and VAC are often used to indicate direct and alternating voltages respectively. Direct current and alternating current have different advantages and disadvantages that make them useful for different applications. Most consumer electronic devices, like cellphones, flat screen TVs and even electronic cars, operate with direct current. If it runs off of battery, if it plugs into an AC wall adapter, or if it gets it's power from a USB cable, it runs on DC.
Alternating current is primarily used to generate and transport power across long distances. The power that comes into your home is carried there over high voltage transmission lines that use alternating current. For devices in your home that operate on direct current, like a flat screen TV, an AC to DC adapter is used to convert the alternating current from a wall outlet to direct current for the device to use.
- Reading electrical schematics
- Building circuits on breadboards
- Reviewing types of static and variable resistors
- Reading resistor color codes
- Measuring resistance with a DMM
- Measuring resistive sensors with an Arduino microcontroller
- Making electrical signal measurements with an oscilloscope
- Measuring AC voltage with a DMM
- Understanding the time domain and frequency domain
- Designing passive low-pass and high-pass filters
- Reviewing reactive RC and RL circuits
- The relationship between capacitors and inductors