Mar. 07, 2024
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Low power. Your device will power down unless plugged into a power outlet.
How many of us have gotten such a warning from one of our digital devices? Looks like it’s time to plug it in and recharge the batteries with electricity.
But what is electricity?
Electricity is the term we use to describe the energy of charged particles. Electricity might be stored, like in a battery. When you connect a battery to a light bulb, electricity flows. This happens because electrical charges (electrons) are free to carry energy from the battery through the bulb. Sometimes electricity is described as the flow of electrons between neighboring atoms.
Several terms help us describe electricity and its potential to do work.
Current refers to the flow of electric charges. That is, how much charge is moving per second. When people talk about electricity, they’re usually referring to electric current.
Currents are measured in units known as amperes, or amps, for short. A single ampere of current is about 6 quintillion electrons per second. (That’s the number 6 followed by 18 zeroes.) For many devices, it’s common to see currents that are only thousandths of an amp, or milliamps.
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Client key* E-mail Address*Voltage offers a gauge of how much electrical energy is available to power devices. Voltage could be stored in a battery or capacitor. You may have seen a 1.5-volt label on AA and AAA batteries. In the United States, every regular electrical outlet supplies 120 volts. Large appliances like refrigerators and some air conditioners are powered by a special outlet. That outlet supplies 220 volts.
Current and voltage are related. To understand how, imagine water flowing downhill in a river. Voltage is like the height of the hill. Current is like the moving water. A tall hill could cause more water to flow. In the same way, a bigger voltage can yield a bigger electrical current.
But the height of a hill isn’t the only thing that affects how the water flows. A wide riverbank would allow lots of water to flow. But if the river is narrow, the path is restricted. Not as much water can get through. And if the river gets clogged with fallen trees, the water might even stop flowing. Just like many factors affect the water’s ability to flow, there are several ways that the flow of electric current can be helped or resisted.
Resistance describes how easily current can flow. A bigger voltage can lead to a bigger current, but more resistance lowers that current. Resistance varies from material to material. It also depends on the condition of a material. For instance, dry skin has a high resistance. Electricity does not easily pass across it. Getting skin wet, however, drops the resistance to almost zero.
It’s important to realize that any amount of resistance may be overwhelmed by too much current trying to pass through it. As an example, electricity will not flow through wood if you simply hold the electrode of a small battery against the trunk of a tree. But a powerful bolt of lightning packs enough energy to split the tree in half.
In this simple circuit, you can see how the circuit is a loop. When the orange copper switch is open (as shown), the loop is not complete and electricity will not flow. When it is closed, electricity can flow from the battery through the circuit to turn on the light bulb.
haryigit/iStock/Getty Images Plus
Circuits describe the paths that electrical currents take. Think of a circuit as a loop. In order for electricity to flow, this loop must remain closed. That means it has no gaps. When you connect a light bulb to a battery, the electricity flows from one end of the battery, through a wire, to the light bulb. Then it flows back to the battery through another wire. The circuit will continue to light the bulb as long as the loop is closed. Cut the wire and there’s no longer a circuit because the path is broken.
Conductors and insulators are types of materials that respond differently to electricity. Conductors have very low resistance, so they can easily transmit a current. Most metals are very good conductors. So is saltwater. (This is why it’s dangerous to go swimming during a lightning storm! The chemicals in a swimming pool and the salts on our bodies make the water an especially good conductor of electricity.)
Insulators, in contrast, strongly resist the flow of electricity through them. Most plastics are insulators. That’s why electrical cords are jacketed in a layer of plastic. Electricity will flow through the copper (metal) wire inside a power cord, but the plastic coating outside makes the cord safe for us to handle.
Electricity flows through the copper wires bundled inside a power cord. The plastic coating jackets the wires so that we can safely touch the cord.
Jose A. Bernat Bacete/Moment/Getty Images Plus
Semiconductors are materials that are in between conductors and insulators. In semiconductors, the flow of electricity can be precisely controlled. That makes these materials useful for directing electrical current, like tiny traffic guards, inside electronics. Computer chips depend on the ability of semiconductors to interact in complex circuits. The most common semiconductor material is the element silicon. (Not to be confused with the silicone found in flexible ice cube trays and baking tools!)
Transformers, as their name suggests, are devices that transform electrical voltage. They can be found in the box-shaped plugs at the end of device chargers. Most of these transformers convert a wall outlet’s 120 volts into a much, much lower level. Why? Household outlets are primed to run high-power appliances such as lamps, toasters, vacuum cleaners or space heaters. But that voltage is far more than smartphones and computers can handle. So the transformer in a charge cord steps down the electricity to a safe level that can run your device without frying it. Each device has its own specific needs for how much voltage it can handle. That’s why it’s important to use the right charging cable for each electronic device.
Electricity can safely power our homes and our devices when used properly. Keep in mind, however, that even common household electricity can cause severe injury or death. Always tell an adult about any broken plugs or cracked electrical wires. Don’t overload circuits by plugging in too many devices at once. Never use electricity near water. And make sure that a device’s power is turned off when changing its batteries. Finally, follow all of the safety warnings that come with electrical devices. It’s better to be safe than to risk injury or fire.
Electricity is the flow of electrical energy through some conductive material. Electronics refers to using changing electrical properties to convey information. Electronic sensors convert some other form of energy (light, heat, sound pressure, etc.) into electrical energy so that we can interpret what’s going on electronically. For example, a microphone changes sound pressure waves in the air to a changing electrical voltage. By amplifying and reading that electrical signal, we can interpret what the sound was that caused it. This process of changing one energy into another is called transduction, and devices that do it are called transducers. Much of the technical work of physical computing is about figuring out what form energy a person is putting out, and what kind of transducer you can buy or build to read that energy. In order to do that, though, it’s necessary to understand a few things about electricity. We’ll start with a few terms we’ll use to refer to electrical properties and components. After that, we’ll talk about the important relationships between some of these terms.
Current is a measure of the magnitude of the flow of electrons in a circuit. It is measured in Amperes, or Amps. Many people explain electrical flow by using water flow as an analogy. Following that analogy, current would be how much water (or electricity) is flowing past a certain point. The higher the amperage, the more water (or electricity) is flowing.
Voltage is a measure of the electrical energy of a circuit. It is measured in Volts. In the water analogy, voltage would be the water pressure. Think of a geyser as high voltage, and the shower of a low-rent apartment on the fifth floor of a tenement building as low voltage (unless you’re one of those lucky people with good water pressure!).
Resistance is a measure of a material’s ability to oppose the flow of electricity. It is measured in Ohms. A sponge in the pipe would act as a resistor, limiting the current (and the voltage) flowing through the pipe.
A circuit is a closed loop containing a source of electrical energy (like a battery) and a load (like a light bulb). Every circuit has to have a load of some sort, All of the electrical energy in a circuit has to get used by the load. The load will convert the electrical energy to some other form of energy. A circuit with no load is called a short circuit. In a short circuit, the power source feeds all of its power through the wires and back to itself, and either the wires melt (if you’re lucky), or the battery blows up, or something else disastrous happens.
Below is a very basic circuit, consisting of a lamp, a switch, and a battery. The electrical energy coming from the battery is converted to heat and light energy by the light bulb.
There are two common kinds of circuits, DC, or Direct Current, and AC, or Alternating Current. In a DC circuit, current always flows one direction. In an AC circuit, poles of the circuit are reversed in a regular repeating cycle. In one part of the cycle, one pole is at a higher potential (positive) and the other is at a lower (negative). In the next part of the cycle, the second pole is more positive, and the first pole is more negative. Most of the circuits we’ll talk about in this class will be DC circuits.Schematic diagrams are diagrams of circuits, with symbols representing the components in the circuit. Many of the typical symbols are shown below.There are two common kinds of circuits, DC, or Direct Current, and AC, or Alternating Current. In a DC circuit, current always flows one direction. In an AC circuit, poles of the circuit are reversed in a regular repeating cycle. In one part of the cycle, one pole is at a higher potential (positive) and the other is at a lower (negative). In the next part of the cycle, the second pole is more positive, and the first pole is more negative. Most of the circuits we’ll talk about in this class will be DC circuits.Schematic diagrams are diagrams of circuits, with symbols representing the components in the circuit. Many of the typical symbols are shown below.
Related articles:Conductors are materials through which electrical current moves freely.
Insulators are materials which prevent the flow of electricity.
Resistors resist, but do not totally block, the flow of electricity. They are used to control the flow of current. Current can move either way through a resistor, so it doesn’t matter which way they’re connected in a circuit. They are symbolized like this:
Capacitors store up electricity while current is flowing into them, then release the energy when the incoming current is removed. Sometimes they are polarized, meaning current can only flow through them in a specific direction, and sometimes they are not. If a capacitor is polarized, it will be marked as such on the diagram. Don’t wire a polarized capacitor backwards; it might explode.
Capacitors are symbolized like this:
Diodes permit the flow of electricity in one direction, and block it in the other direction. Because of this, they can only be placed in a circuit in one direction. They are symbolized like this:
Light-Emitting Diodes (LED’s) are special types of diodes which emit light when current flows through them. They are symbolized like this:
There are many other types of components which you’ll come across:
Voltage (V), Current (I), and Resistance are related (R) are all related, by the following formula:
Volts = Amps x Ohms, or
V = I x R
Current (I), voltage (V), and resistance (R) are also related to electrical power (P) (measured in watts), as follows: Watts = Volts x Amps or
W = V x A
Electrical current flows from places of higher potential energy to places of lower potential energy (i.e. from positive to negative).
Ground is the place in a circuit with where the potential energy of the electrons is zero. Sometimes this point is connected to the actual ground, either through a grounded electrical circuit, water pipe, or some other method. Basically, any conductor that goes to the earth will do.
A few important rules:
Current follows the path of least resistance to the ground. So if it has a choice of two paths in a circuit, and one has less resistance, that’s the path it’ll take.
In any given circuit, the total voltage around the path of the circuit is zero. Each component that offers a resistance lowers the voltage, and by the time we reach the end of the circuit loop, there will be no voltage left.
The amount of current going into any point in a circuit is the same as the amount coming out of that point.
These last two rules give us a way to figure out what’s going on when we put components in a circuit. When we look at how components in a circuit are placed in relation to each other, there are two ways we can do it: one in line after another, or side by side. When they are one in line after another, we say the components are in series with one another. Side by side, they are in parallel with one another.
Let’s look at how the current and voltage changes when components are in series or in parallel:
When two components are in series, they are placed one after another, like so:
When resistors are in series, the voltage drops across each resistor, and the total resistance is equal to the sum of all the resistors. We know in the above circuit, the current anywhere is constant. We know the voltage drops across each resistor, and we know that the total of all the voltage drops equals the voltage across the battery. So Vin = V1 + V2. If we know the values of the resistors, we can use the formula V= I x R to calculate the exact voltages at each point.When two components are in parallel, they are placed beside each other, like this:When resistors are in series, the voltage drops across each resistor, and the total resistance is equal to the sum of all the resistors. We know in the above circuit, the current anywhere is constant. We know the voltage drops across each resistor, and we know that the total of all the voltage drops equals the voltage across the battery. So V= V+ V. If we know the values of the resistors, we can use the formula V= I x R to calculate the exact voltages at each point.When two components are in parallel, they are placed beside each other, like this:
For resistors in parallel, the voltage across them is equal, but the current is divided between them. The total current is constant, however, so we know that the divided current across the parallel resistors is equal to the total current. So I1 + I2 = Itotal.
Though it’s sometimes useful to think about the mathematical relationships of parallel and series circuits, it’s often more useful to think about them in terms of practical effects. Again, think of the water metaphor. For the series example, if one resistor lowers the voltage (water pressure), only a smaller voltage (trickle of water) gets through to the next. For the parallel example, the amount of water from the main stream (total current) gets divided into two streams, but the total amount of water flowing through those two streams is equal to the original amount of water. Keeping in mind these basic relationships will help you figure out what the effect of one component is on another when you see them in a circuit together, even if you don’t know (or care about) their precise mathematical relationship.
When you’re ready to begin building circuits, read the notes on breadboards for a quick introduction to how to use a solderless breadboard.
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