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.
When an atom has the same number of protons and electrons, they cancel each other out.
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.
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 static from rubbing a balloon on your head is caused by the transfer of electrons.
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!
Lightening is created when electrons move quickly from one object to another through the air.
When electric charge accumulates on an object, such as on the balloon, we call this static electricity. The term 'static' simply refers to the fact that the electric charge doesn't move around but instead stays on the balloon. Have you ever been zapped by static electricity? I'll bet you have and there's nothing 'static' about that! To understand why this happens, let's take a look at our balloon example again. When the balloon was rubbed against your hair, it accumulated a whole bunch of electrons. Now, let's say we bring the balloon close to an object with a positive charge. The electrons on the balloon will simultaneously be attracted to the positively charged object and repelled from each other. If the attractive and repulsive forces are strong enough, the electrons will jump straight through the air to get to the positively charged object. This rapid transfer of electrons is what you see, hear, and feel as an electric spark. On a larger scale, this is exactly the same phenomenon that causes lightning.
Let's review what we've learned. The electric charge possessed by electrons and protons is responsible for the form of energy called electricity. Protons have a positive charge, and electrons have an equal amount of negative charge. When an atom with no net charge gains or loses an electron, it becomes an ion. Electrons can be transferred from the atoms of one object to the atoms of another object. This transfer of electrons leaves one object positively charged, while the other object becomes negatively charged. The conservation of charge states that charge is neither created nor destroyed but only transferred. Objects with opposite charges exert an attractive force on each other, while objects with similar charges exert a repulsive force on each other. And finally, static electricity is the stationary accumulation of charge on an object that can result in a spark, which is the rapid transfer of electrons between objects.
Upon completion of this lesson, you should be ready to:
- Explain how protons and electrons can create electric charge
- Summarize how rubbing a balloon on your hair makes your hair stand up
- Define electricity, ion, conservation of charge, and static electricity
Electric Charge and Electric Force
Electric charges feel forces from other electric charges, electric fields, and when they move through magnetic fields at any angle other than 0° or 180° to the magnetic field lines. Let's practice working on solving problems involving electric charges. Answer the questions and then compare your answers to the ones provided.
Practice with Electric Charge and Electric Force
1. What happens to two positive charges that are near each other?
2. What happens to two negative charges that are near each other?
3. What happens to a positive charge that is placed near a negative charge?
4. What is the result when a negative charge is placed near a piece of foam with no electric charge?
5. What is required to keep two positive charges close together?
6. What causes an object to become positively charged?
1. The positive charges repel each other and move in opposite directions.
2. The negative charges repel each other and move in opposite directions.
3. The opposite charges attract each other and move towards each other.
4. Nothing happens because the foam does not have a charge.
5. An external force has to be applied to both of the charges to keep them close together.
6. Rubbing off electrons from an object causes the object to become positively charged. This is because electrons are free to move and be removed from an object while protons in the nucleus are pretty much bound inside the nucleus.