Electricity

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Lightning: electricity in nature

Electricity occurs when electric charge flows. It is an energy source which we use to power machines and electrical devices.

We see electricity when the number of electrons an atom has are either more than usual or less than usual. If the electrons stay where they are, the atom that has too many or too few electrons will attract or sometimes repel other atoms. If the electrons move from where there are too many to where there are too few, then we will see a flow of electrons, an electrical current.

There is electricity in nature as well as electricity that is human-made. We see electricity in nature as lightning, and as the way some things attract each other and stick together.

Scientists have found we can make electricity if we pass a magnet close to a metal wire, or if we put the right chemicals in a jar with two different kinds of metal rods. We can also make static electricity by rubbing two things, for instance a wool cap and a plastic ruler, together. This may make a spark.

Scientists have observed that electricity can flow like water from one place to another, either as a spark or as a current in a metal. They now know that all matter has an electric charge, but this is mostly cancelled out by the presence of matter with an opposite charge. We only see an effect when there is too much or too little electric charge in one place so that it is not cancelled out.

Since the nineteenth century, electricity has been used in every part of our lives. Until then, it was just a curiosity or a force of nature seen in a thunderstorm.

People make most our electric energy in generators. The biggest generators are in power stations. Some of our electricity comes from photovoltaic cells or from batteries.

Electricity arrives at our homes through wires from the places where it is made. It is used by electric lamps for producing light, electric heaters to produce heat, etc. It is also used by many devices such as washing machines, electric cookers, etc. for doing work. In factories, electricity is used for running machines and computers.

The people who deal with electricity and electrical devices in our homes and factories are called "electricians".

Electricity in physics[change | change source]

Electricity works because electric charges push and pull on each other. There are two types of electric charges: positive charges and negative charges. Similar charges repel each other. This means that if you put two positive charges close together and let them go, they would move apart. Two negative charges also repel. But different charges attract each other. This means that if you put a positive charge and a negative charge close together, they would smack together. A short way to remember this is the phrase opposites attract, likes repel.

Electric charges push or pull on each other if they are not touching. This is possible because each charge makes an electric field around itself. An electric field is an area that surrounds a charge. At each point near a charge, the electric field points in a certain direction. If a positive charge is put at that point, it will be pushed in that direction. If a negative charge is put at that point, it will be pushed in the exact opposite direction.

All the matter in the world is made of tiny positive and negative charges. The positive charges are called protons, and the negative charges are called electrons. Protons are much bigger and heavier than electrons, but they both have the same amount of electric charge, except that protons are positive and electrons are negative. Because "opposites attract," protons and electrons stick together. A few protons and electrons can form bigger particles called atoms and molecules. Atoms and molecules are still very tiny. It is impossible to see them without a very powerful microscope. Any big object, like your body, has more atoms and molecules in it than anyone could count.

Because negative electrons and positive protons stick together to make big objects, all big objects that we can see and feel are electrically neutral. Electrically is a word meaning "describing electricity", and neutral is a word meaning "balanced." That is why we do not feel objects pushing and pulling on us from a distance, like they would if everything was electrically charged. All big objects are electrically neutral because there is exactly the same amount of positive and negative charge in the world. We could say that the world is exactly balanced, or neutral. This seems very surprising and lucky. Scientists still do not know why this is so, even though they have been studying electricity for a long time.

Electric current[change | change source]

A drawing of an electrical circuit: the current (I) flows from + round the circuit back to -
Electricity is sent on wires.

In some materials, electrons are stuck tightly in place, while in other materials, electrons can move all around the material. Protons never move around a solid object because they are so heavy, at least compared to the electrons. A material that lets electrons move around is called a conductor. A material that keeps each electron tightly in place is called an insulator. Examples of conductors are copper, aluminum, silver, and gold. Examples of insulators are rubber, plastic, and wood. Copper is used very often as a conductor because it is a very good conductor and there is so much of it in the world. But sometimes, other materials are used.

Inside a conductor, electrons bounce around, but they do not keep going in one direction for long. If an electric field is set up inside the conductor, the electrons will all start to move in the direction opposite to the direction the field is pointing (because electrons are negatively charged). A battery can make an electric field inside a conductor. If both ends of a piece of wire are connected to the two ends of a battery (called the electrodes), the loop that was made is called an electrical circuit. Electrons will flow around and around the circuit as long as the battery is making an electric field inside the wire. This flow of electrons around the circuit is called electric current.

A conducting wire used to carry electric current is often wrapped in an insulator such as rubber. This is because wires that carry current are very dangerous. If a person or an animal touched a bare wire carrying current, they could get hurt or even die depending on how strong the current was. You should be careful around electrical sockets and bare wires that might be carrying current.

It is possible to connect an electrical device to a circuit so that electrical current will flow through a device. This current will make the device do something that we want it to do. Electrical devices can be very simple. For example, in a light bulb, current flows through a special wire called a filament, which makes it glow. Electrical devices can also be very complicated. Electricity can be used to drive an electric motor inside a tool like a drill or a pencil sharpener. Electricity is also used to power modern electronic devices, including telephones, computers, and televisions.

Some terms related to electricity[change | change source]

  • Electric voltage is the "push" behind the current. It is the amount of work per electric charge that an electric source can do. When 1 coulomb of electricity has 1 joule of energy, it will have 1 volt of electric potential.
  • Electrical resistance is the ability of a substance to resist the flowing of the current, i.e. to reduce the amount of current that flows through the substance. If an electric voltage of 1 volt maintains a current of 1 ampere through a wire, the resistance of the wire is 1 ohm. When the flow of current is opposed (resisted) energy gets used or gets converted to other forms (e.g. heat, etc.).
  • Electric energy is the ability to do work by means of electric devices. Electric energy is a "conserved" property, meaning that it behaves like a substance and can be moved from place to place. Electric energy is measured in joules or kilowatt-hours (kW h).
  • Electric power is the rate at which electric energy is being used, stored, or transferred. Flows of electrical energy along power lines are measured in watts. If the electric energy is being converted to another form of energy, it is measured in watts. If it is stored (as in electric or magnetic fields), it is measured in volt-amperes reactive. If some of it is converted and some of it is stored, it is measured in volt-amperes.

Methods of generating electricity[change | change source]

Electricity is made in power stations.

Electricity is mostly generated in places called power stations. Power stations use heat to turn water into steam. The force of the steam pressure turns giant fan-like structures called turbines, which are linked to machines called 'generators'. Generator have a head with wires which spins inside a magnetic field. Electromagnetic induction causes electricity to flow through the wires.

There are many sources of heat which can be used to generate electricity. Heat sources can be classified into two types: renewable energy resources in which the supply of heat energy never runs out and non-renewable energy resources in which the supply will be eventually used up.

Sometimes, a natural flow such as wind power or water power can be used to directly turn a generator so no heat is needed.

Renewable energy resources[change | change source]

Renewable heat energy
Renewable flow energy

Non-renewable energy resources[change | change source]

These all use heat as a source of energy.

Solid-state electricity sources[change | change source]

These sources have no moving parts. They are more expensive than generators, and are used where other questions are more important.