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Electricity

Science of Electricity

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Science of Electricity Basics

Everything is made of atoms

To understand electricity, it's important to know something about atoms. Atoms are the building blocks of the universe. Everything in the universe is made of atoms—every star, every tree, and every animal. The human body is made of atoms. Air and water are made of atoms, too. Atoms are so small that millions of them would fit on the head of a pin.

Atoms are made of even smaller particles

The center of an atom is called the nucleus. The nucleus is made of particles called protons and neutrons. Electrons spin around the nucleus in shells a great distance from the nucleus. If the nucleus was the size of a tennis ball, the atom would be the size of a sphere about 1,450 feet in diameter, or about the size of one of the largest sports stadiums in the world. Atoms are mostly empty space.

Graph of an atom

If the naked eye could see an atom, it would look a little like a tiny center of balls surrounded by giant invisible bubbles (or shells). The electrons would be on the surface of the bubbles, constantly spinning and moving to stay as far away from each other as possible. Electrons are held in their shells by an electrical force.

The protons and electrons of an atom are attracted to each other. They both carry an electrical charge. Protons have a positive charge (+) and electrons have a negative charge (-). The positive charge of the protons is equal to the negative charge of the electrons. Opposite charges attract each other. An atom is in balance when it has an equal number of protons and electrons. The neutrons carry no charge and their number can vary.

The number of protons in an atom determines the kind of atom, or element, it is. An element is a substance consisting of one type of atom (the Periodic Table shows all the known elements), all with the same number of protons. Every atom of hydrogen, for example, has one proton, and every atom of carbon has six protons. The number of protons determines which element an atom is.

Electricity is the movement of electrons between atoms

Graph showing movement of electrons

Electrons usually remain a constant distance from the atom's nucleus in precise shells. The shell closest to the nucleus can hold two electrons. The next shell can hold up to eight. The outer shells can hold even more. Some atoms with many protons can have as many as seven shells with electrons in them.

The electrons in the shells closest to the nucleus have a strong force of attraction to the protons. Sometimes, the electrons in an atom's outermost shells do not have a strong force of attraction to the protons. These electrons can be pushed out of their orbits. Applying a force can make them shift from one atom to another. These shifting electrons are electricity.

Static electricity exists in nature

Lightning is a form of electricity. Lightning is electrons moving from one cloud to another or electrons jumping from a cloud to the ground. Have you ever felt a shock when you touched an object after walking across a carpet? A stream of electrons jumped to you from that object. This is called static electricity.

Have you ever made your hair stand straight up by rubbing a balloon on it? If so, you rubbed some electrons off the balloon. The electrons moved into your hair from the balloon. The electrons tried to get far away from each other by moving to the ends of your hair. They pushed against or repelled each other and made your hair move. Just as opposite charges attract each other, like charges repel each other.

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Magnets and Electricity

Magnetic Field Around a Bar Magnet
Magnetic field around a bar magnet
graph showing magnetic repulsion
Graph showing magnetic attraction

Source: National Energy Education Development Project (public domain)

The spinning of the electrons around the nucleus of an atom creates a tiny magnetic field. The electrons in most objects spin in random directions, and their magnetic forces cancel each other out.

Magnets are different because the molecules in magnets are arranged so that their electrons spin in the same direction. This arrangement and movement creates a magnetic force that flows out from a north-seeking pole and from a south-seeking pole. This magnetic force creates a magnetic field around a magnet.

Have you ever held two magnets close to each other? They don't act like most objects. If you try to push the two north poles or two south poles together, they repel each other. But if you put a north pole and a south pole together, the magnets will stick together because the north and south poles attract each other. Just like protons and electrons—opposites attract in magnets.

Magnetic fields can be used to make electricity

The properties of magnets are used to make electricity. Moving magnetic fields pull and push electrons. Metals such as copper and aluminum have electrons that are loosely held. Moving a magnet around a coil of wire, or moving a coil of wire around a magnet, pushes the electrons in the wire and creates an electrical current. Electricity generators essentially convert kinetic energy (the energy of motion) into electrical energy.

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Batteries, Circuits, & Transformers

Batteries produce electricity

image of battery and light bulb

Source: Adapted from National Energy Education Development Project (public domain)

An electrochemical battery produces electricity with two different metals in a chemical substance called an electrolyte. One end of the battery is attached to one of the metals, and the other end is attached to the other metal. A chemical reaction between the metals and the electrolyte frees more electrons in one metal than it does in the other.

The metal that frees more electrons develops a positive charge, and the other develops a negative charge. If an electrical conductor, or wire, connects one end of the battery to the other, electrons flow through the wire to balance the electrical charge.

An electrical load is a device that uses electricity to do work or to perform a job. If an electrical load—such as an incandescent light bulb—is placed along the wire, the electricity can do work as it flows through the wire. Electrons flow from the negative end of the battery through the wire to the light bulb. The electricity flows through the wire in the light bulb and back to the positive end of the battery.

Electricity travels in circuits

Electricity must have a complete path, or electrical circuit, before the electrons can move. If a circuit is open, the electrons cannot flow. Turning on a light switch closes a circuit. The electricity flows from an electric wire, through the light bulb, and back out another wire. An incandescent light bulb produces light as electricity flows through a tiny wire in the bulb, which gets very hot and glows.

Turning off a light switch opens the circuit and no electricity flows to the light. An incandescent light bulb burns out when the tiny wire inside the bulb breaks, which opens the circuit. The switch or on-off button on all electrical devices closes (turns on) or opens (turns off) an electrical circuit in the device.

image showing open and closed circuits in a light bulb

Source: Adapted from National Energy Education Development Project (public domain)

Transformers help to move electricity efficiently over long distances

To solve the problem of sending electricity over long distances, William Stanley developed a device called a transformer. A transformer changes the voltage of electricity in a conductor or power line. High-voltage transmission lines, like those that hang between tall metal towers, carry electricity over long distances to where it is needed. Higher voltage electricity is more efficient and less expensive for long distance electricity transmission. Lower voltage electricity is safer for use in homes and businesses. Transformers increase (step up) or reduce (step down) voltages as electricity moves from power plants to homes and businesses.

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Measuring Electricity

Electricity is measured in Watts and kilowatts

A mechanical electricity meter
Picture of a residential electricity meter.

Source: Stock photography (copyrighted)

A smart electricity meter
Picture of a smart meter.

Source: Stock photography (copyrighted)

Electricity is measured in units of power called Watts, named to honor James Watt, the inventor of the steam engine. A Watt is the unit of electrical power equal to one ampere under the pressure of one volt.

One Watt is a small amount of power. Some devices require only a few Watts to operate, and other devices require larger amounts. The power consumption of small devices is usually measured in Watts, and the power consumption of larger devices is measured in kilowatts (kW), or 1,000 Watts.

Electricity generation capacity is often measured in multiples of kilowatts, such as megawatts (MW) and gigawatts (GW). One MW is 1,000 kW, and one GW is 1,000 MW.

Electricity use over time is measured in Watthours

A Watthour (Wh) is equal to the energy of one Watt steadily supplied to, or taken from, an electric circuit for one hour. The amount of electricity that a power plant generates or an electric utility customer uses over a period of time is typically measured in kilowatthours (kWh), which is the number of kilowatts generated or consumed over one hour. For example, if you use a 40-Watt (0.04 kW) light bulb for five hours, you have used 200 Wh, or 0.2 kWh, of electrical energy.

Utility companies measure and monitor electricity use with meters

Electric utilities measure the electricity consumption of their customers with meters that are usually located on the outside of the customer's property where the power line enters the property. In the past, all electricity meters were mechanical devices that a utility employee had to read manually. Eventually, automated reader devices became available. These meters periodically report electricity use to utilities from mechanical meters with an electronic signal. Now, many utilities use electronic smart meters, which provide wireless access to the meter's power usage data, to measure electricity consumption on a real-time basis. Some smart meters can even measure the electricity use of individual devices and allow the utility or customer to control electricity use remotely.

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How Electricity is Generated

How electricity is generated

Turbine generator Diagram of a turbine generator - Spinning rotor turning coiled copper wir inside stationary magnets to generate electricity.

Source: Adapted from Energy for Keeps (public domain)

In 1831, scientist Michael Faraday discovered that when a magnet is moved inside a coil of wire, an electric current flows in the wire. An electricity generator is a device that converts a form of energy into electricity. Generators operate because of the relationship between magnetism and electricity. Generators that convert kinetic (mechanical) energy into electrical energy produce nearly all of the electricity that consumers use.

A common method of producing electricity is from generators with an electromagnet—a magnet produced by electricity—not a traditional magnet. The generator has a series of insulated coils of wire that form a stationary cylinder. This cylinder surrounds a rotary electromagnetic shaft. When the electromagnetic shaft rotates, it induces a small electric current in each section of the wire coil. Each section of the wire coil becomes a small, separate electric conductor. The small currents of the individual sections combine to form one large current. This current is the electricity that moves through power lines from generators to consumers.

An electric power plant uses a turbine or similar machine to drive these types of generators. Different types of turbines include steam turbines, gas combustion turbines, water turbines, and wind turbines.

A turbine converts the kinetic energy of a moving fluid (liquid or gas) to mechanical energy. In a turbine generator, a moving fluid pushes a series of blades mounted on a shaft, which rotates the shaft connected to a generator. The generator, in turn, converts the mechanical energy to electrical energy based on the relationship between magnetism and electricity.

In 2016, about 65% of total U.S. electricity generation was from steam turbines that use biomass, coal, geothermal energy, natural gas, nuclear energy, and solar thermal energy. These types of power plants are about 33% efficient, which means that for every 100 units of primary heat energy that goes into a power plant, only 33 units are converted to useable electrical energy.

Other types of devices that generate or produce electricity include electrochemical batteries, fuel cells, solar photovoltaic cells, and thermoelectric generators.