Electric Charge and Force: Definition, Repulsion & Attraction

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• 0:05 Atoms and Electric Charge
• 1:28 Ions
• 2:07 Conservation of Charge
• 3:25 Forces Between Charged…
• 4:15 Static Electricity
• 5:32 Lesson Summary

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Lesson Transcript
Instructor: Jim Heald

Jim has taught undergraduate engineering courses and has a master's degree in mechanical engineering.

Have you ever wondered what electricity is and where it comes from? Have you ever been zapped by static electricity and wondered how it got there? We'll answer all of these questions in this lesson on electric charge and force!

Atoms and Electric Charge

You probably know what happens if you rub a balloon against your hair. When you take the balloon away, some of your hair stands straight up, as if it's trying to follow the balloon. You may even know that it's caused by something called static electricity. But do you know what static electricity is or why it makes your hair become attracted to the balloon? To answer these questions, we have to start with the atom.

Everything in the universe is made of atoms, and every atom contains three types of particles called protons, neutrons, and electrons. The protons and neutrons are packed together in the nucleus at the center of the atom, while the electrons zip around the outside in a constant motion. For our discussion on electricity, we only need to concern ourselves with protons and electrons because they have a property called electric charge.

The electric charge that electrons and protons possess is responsible for the form of energy that we commonly call electricity. Protons have a positive charge, which is easy to remember because the word 'proton' and 'positive' both start with the letter 'p.' Electrons on the other hand have a negative charge, which is equal but opposite to the charge on a proton. If you bring one electron and one proton together, their charges cancel each other out, and we say that together they have no net charge.

Ions

In most atoms, there are equal numbers of protons and electrons, so the atom itself has no net charge. However, there are many atoms that either give away electrons or accept more electrons with relative ease. When this happens, we call the atom an ion. If an electron goes away, then the atom is left with more protons than electrons, and the atom becomes a positive ion. Likewise, if an electron comes along and joins the atom, then there will be more electrons than there are protons, and the atom will become a negative ion.

Conservation Of Charge

The transfer of electrons from one atom to another happens all the time. Remember rubbing a balloon on your hair? This is a great example of transferring electrons, but why does it happen? The answer is your hair contains atoms that are happy to give away some of their electrons. On the other hand, the balloon contains atoms that want to accept those electrons and hold onto them. Therefore, when you rubbed the two together, a bunch of electrons transferred from your hair onto the balloon. As a result of this transfer, your hair became positively charged because its atoms were left with more protons than electrons, and the balloon became negatively charged because its atoms had more electrons than protons.

A very important observation from this example is that we didn't make more electrons to build up a negative charge on the balloon, and we didn't destroy any electrons to build up a positive charge on your hair. All we did was transfer the electrons from one place to another. This concept is known as the conservation of charge. Simply stated, charge is neither created nor destroyed. It only transfers from one place to another.

Forces Between Charged Particles

Let's talk about why your hair was attracted to the balloon after they were rubbed together. Have you ever heard the saying, 'opposites attract?' A very important phenomenon of charged particles is that opposite charges exert a force on each other that tends to pull them together. Because your hair was positively charged and the balloon was negatively charged, they did in fact become attracted to each other. Now, if you take the balloon away completely, you might observe that some of your hairs won't lay back down on your head but instead stick straight up in the air. This observation demonstrates the other phenomenon that similar charges exert a force on each other that tends to push them away. All of your hairs are positively charged, so they're trying their best to stay away from each other!

Static Electricity

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