How do dc circuits work

Mountain Time:. Why, Alternating Current and Direct Current, of course! Both AC and DC describe types of current flow in a circuit. In direct current DC , the electric charge current only flows in one direction.

Electric charge in alternating current AC , on the other hand, changes direction periodically. The voltage in AC circuits also periodically reverses because the current changes direction. Most of the digital electronics that you build will use DC. However, it is important to understand some AC concepts. AC also has some useful properties, such as being able to convert voltage levels with a single component a transformer , which is why AC was chosen as the primary means to transmit electricity over long distances.

Alternating current describes the flow of charge that changes direction periodically. As a result, the voltage level also reverses along with the current. AC is used to deliver power to houses, office buildings, etc. AC can be produced using a device called an alternator. This device is a special type of electrical generator designed to produce alternating current.

A loop of wire is spun inside of a magnetic field, which induces a current along the wire. The rotation of the wire can come from any number of means: a wind turbine, a steam turbine, flowing water, and so on. Because the wire spins and enters a different magnetic polarity periodically, the voltage and current alternates on the wire. Here is a short animation showing this principle:.

Generating AC can be compared to our previous water analogy :. To generate AC in a set of water pipes, we connect a mechanical crank to a piston that moves water in the pipes back and forth our "alternating" current. Notice that the pinched section of pipe still provides resistance to the flow of water regardless of the direction of flow. AC can come in a number of forms, as long as the voltage and current are alternating. If we hook up an oscilloscope to a circuit with AC and plot its voltage over time, we might see a number of different waveforms.

The most common type of AC is the sine wave. The AC in most homes and offices have an oscillating voltage that produces a sine wave. Triangle waves are found in sound synthesis and are useful for testing linear electronics like amplifiers. We often want to describe an AC waveform in mathematical terms.

For this example, we will use the common sine wave. There are three parts to a sine wave: amplitude, frequency, and phase. V t is our voltage as a function of time, which means that our voltage changes as time changes. The equation to the right of the equals sign describes how the voltage changes over time. V P is the amplitude. The sin function indicates that our voltage will be in the form of a periodic sine wave, which is a smooth oscillation around 0V. Rising Sea Level. Direct current Figure 1: An animation from a PhET simulation [1] of direct current which has been slowed down considerably.

See alternating current for a comparison. NJ: Prentice-Hall, , ch. Contact us About us Privacy policy Terms of use. Direct current systems are also easier to understand than systems using alternating current AC but AC systems rely on many of the same principles and circuit components as DC systems.

DC Circuits are the basic building block of many electronics, and are the best way to begin to understand electrical circuits. For electronics, there are fundamental theoretical principles, as well as components that function by making practical use of the theory.

For example, resistors are circuit components that rely on the principle of electrical resistance in order to function. A simple circuit can be described as a closed loop connected to a power source. The power source provides a voltage electric potential that pushes electrons around the loop. The electrons flow through the whole circuit, which is usually made of conductors and devices like resistors , capacitors , or inductors.

Electron flow is called electric current. Electrons actually flow in the opposite direction of current, and we usually think about current flow, not electron flow. This is where the name Direct Current DC comes from.

A direct current circuit is one in which the current only flows in one direction. In other words in a DC circuit, the flow of electricity goes in one direction; from the positive terminal to the negative terminal. In a DC circuit, the value of the voltage might change. For instance, the voltage across the circuit might alternate from.

But the polarity of voltage, or direction of current flow never changes; it always goes in the same direction. To put this into perspective, AC circuits feature an Alternating Current , in which the direction of current switches from one side to the other. Direct Current DC always pushes the electrons along in the same direction, but alternating current AC pushes electrons one way and then pulls them back in the other direction. For now just keep in mind that in a DC circuit, the current always flows in one direction; in an AC circuit the current alternates and flows back and forth within a circuit.

In order for electricity to flow through a circuit, it must have somewhere to come from and somewhere to go. For instance, a wire in the circuit is no longer making contact on one side.

This is called an open circuit. Open circuits are otherwise complete circuits that have a break somewhere, preventing current from flowing. DC Circuits are made up of two main things: components , and conductors.

Perhaps the most important component is the power source. Without a power source, there would be nothing to drive current in the circuit at all. DC circuits are powered by direct current sources , which are power sources that generate a potential difference voltage between two points.

If we were to separate some electrons from their atoms and then connect the electrons, through conductors , back to their original atoms, we would have a DC circuit.

The separation between the negatively charged electrons and positively charged atoms ions results in a difference of electric potential voltage. This resistance is similar to the friction of the hose against the water moving through it. Although static electricity can be discharged through a metal wire, it is not a continuous source of DC electricity.

Instead, batteries and DC generators are used to create DC. The automobile battery consists of lead plates in a sulfuric acid solution. When the plates are given a charge from the car's generator or alternator, they change chemically and hold the charge. That source of DC electricity can then be used to power the car's lights and such. The biggest problem with this type of battery is that sulfuric acid is very caustic and dangerous.

Another battery that you can make yourself is a lemon battery. This one needs no charging but depends on the acidic reaction of different metals. Copper and zinc work the best. You can use a copper penny or copper piece of wire. A zinc-coated or galvanized nail can be used as the other terminal. A standard iron nail will work, but not as good. Push the copper wire and galvanized nail into an ordinary lemon and measure the voltage across the metals with a voltmeter.