# Electric Charge

by Ron Kurtus (updated 19 June 2016)

One property of matter is the electric charge. Most subatomic particles have either a positive (+) or negative (−) electric charge. Those that don't are considered neutral.

The most common charged particles are the electron and proton. Atoms with an excess of electrons are called negative ions. Those with missing electrons are called positive ions.

There is an electric field that flows between opposite charges, causing an electric force. This results in an attractive force between the opposite charges and a repelling force between like charges.

Note: The electric charge unit is the coulomb, which is equal to the charge of approximately 6.241×1018 electrons.

Questions you may have include:

• Which particles have charges?
• What does the electric field look like?
• What does the electric force do?

This lesson will answer those questions. Useful tool: Units Conversion

## Charged particles

An atom is comprised of a nucleus consisting of protons and neutrons and a collection of electrons in orbits or shells around the nucleus. Protons, neutrons and electrons are the most common sub-atomic particles.

Sub-atomic particles have a positive (+) electric charge, a negative (−) electric charge, or no electric charge at all. For example, a proton has a positive electric charge, an electron has a negative electric charge, and a neutron is neutral and has no electric charge.

### Ions

An atom typically has the same number of negative charged electrons as positive charged protons, so its total charge is neutral. But if the atom loses some electrons, it will have more positive charges than negative charges and is called a positive ion. Likewise, if the atom gains an excess of electrons, it is called a negative ion.

Ions are charged particles. They are often involved in static electricity and electric current on electrolyte solutions such as salt water.

### Unipoles

Electricly charged particles are called unipoles, in that they can exist by themselves ("uni" means one). This is different than the case of magnetic poles, where for every N pole, there must be an S pole. Magnets are called dipoles, meaning they must have two poles.

### Anti-matter

There is duality in the Universe. That means if there is a left hand, there will be a right hand. That also works with particles.

Since there is a negative charged electron, there is also a version with a positive charge. That anti-electron particle is called the positron. It is the same size and weight as an electron, except it has an opposite charge.

For the positive charged proton, there is the anti-proton that has a negative charge. These oppositely charged particles are called anti-matter.

There is even an anti-neutron. It is still neutral in electric charge, but it spins in the opposite direction.

## Electric field

An electric field surrounds every particle that has an electric charge. By convention, the lines of the electric field are said to radiate from a (+) particle and move towards a (−) particle. It is not certain if there is any direction of radiation, and there is no real good explanation of what the electric field is made of. It's just there.

Electric field lines shown moving from a positive particle

When a positive charged particle (+) like a proton is near a negative charged particle (−) like an electron, the electric field goes from one to the other.

Electric field direction from (+) to (−)

## Forces acting on charged particles

The electric field acts like a force at a distance and the lines are considered lines of force.

### Opposite charges attract

When a positive charged particle is near a negative charged particle, they are attracted to each other by the lines of force.

#### Static electricity

Static electricity is a good example of opposite charges attracting. If electrons are collected on the surface of one material and positive ions are collected on another surface, the negative and positive charges attract. Either the materials are pulled together or a stream of electrons jumps the gap as a spark.

Note that since protons are in the nucleus, they never collect on a surface in static electricity. Rather, they contribute to the charge of the ions that have lost electrons.

#### Colliding with anti-matter

If an electron would come near its anti-matter twin, the positron, they would be attracted to each other until they collide. Then they would each be annihilated with a large amount of energy given off in the form of electromagnetic radiation and other smaller sub-atomic particles moving at a high speed. Likewise, if a proton comes into contact with an anti-proton, they will annihilate, giving off a large amount of energy.

#### Not colliding with other matter

Although they have opposite charges and are attracted to each other, an electron will never combine with a proton. The reason has to do with other forces being involved that keep them apart, as explained in Quantum Theory. This is the same reason that electrons don't go crashing into the positive charged atomic nucleus.

### Like charges repel

When particles have the same charge, they repel each other.

Like charges push away from each other

This can be seen in a static electricity experiment. Attach strings to two balloons and rub them both on a wool sweater. Then when you hang the balloons next to each other, you can see the electric forces push them apart.

## Summary

An important property of matter is electric charge. Most sub-atomic particles have either a positive (+) or negative (−) electric charge. Those that don't are considered neutral. Atoms with an excess of electrons or are missing electrons are called ions. There is an electric field that flows between the positive to negative charges, resulting in an attractive force between the two. Opposite charges attract and like charges repel.

Be good at taking tests

## Resources and references

Ron Kurtus' Credentials

### Websites

Electric charge and Coulomb's law - From Boston University lecture notes

Electric Charge - Overview of charges, including history, from Wikipedia free encyclopedia

Electric Field - Wikipedia

Electrostatics - Wikipedia

DC and AC Electricity Resources

Physics Resources

### Books

(Notice: The School for Champions may earn commissions from book purchases)

Schaum's Outline of Basic Electricity by Milton Gussow; McGraw-Hill Trade; (1983) \$18.95 - Explanations of aspects of electricity with sample problems and solutions

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www.school-for-champions.com/science/
electric_charge.htm

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