Elementary Charge: Definition & Overview

Instructor: Betsy Chesnutt

Betsy teaches college physics, biology, and engineering and has a Ph.D. in Biomedical Engineering

What is the smallest amount of charge that can exist? In this lesson, learn the answer to the question! You will also learn about which atomic particles are charged and how charge is transferred from one object to another.

What Is Charge?

Have you ever reached out to touch a metal doorknob when a spark suddenly jumped between your hand and the doorknob, giving you a little shock? Or maybe you've brushed your hair on a cold, dry day and, afterwards, saw that your hair was standing up? What's going on to cause these things to happen?

It's all due to a phenomenon called static electricity. When you brushed your hair, some charged particles were transferred from your hair onto the brush, making your hair charged and causing the individual strands to repel one another.

It's easy to see what happens to your hair and to understand that some charges are being transferred to cause this effect. However, determining exactly what particles are carrying this charge and how much charge these individual particles have is much more complex.

What is the smallest amount of charge that can exist, and what particles can carry this charge?

These are questions that have fascinated people for many years, but it took a long time and a lot of research to find the answers.

What Is the Elementary Charge?

In 1897, JJ Thomson discovered the existence of a tiny charged particle, which he called an electron. He showed that electrons were negatively charged, and that they could transmit negative charges by moving from one object to another. He still wasn't able to determine exactly how much charge each electron had, though.

A few years later, in 1909, Robert Millikan came up with a very clever way to determine the magnitude of a charge on a single electron, which we now call the elementary charge. By using an electric field to suspend charged drops of oil, he was able to calculate the charge on each drop.

Millikan used this device to measure the elementary charge by suspending drops of oil in an electric field
Millikan oil drop apparatus

He measured the charge on hundreds of oil drops and found that each drop's charge was a multiple of 1.6 x 10-19 Coulombs (C). He concluded that the magnitude of charge on the smallest particle that could be transferred, a single electron, must be exactly 1.6 x 10-19 C.

Over 100 years later, we have measured the elementary charge even more precisely than Millikan was able to. The current accepted value for the elementary charge is 1.602176565 x 10-19 C, although 1.6 x 10-19 C usually gives you results that are accurate enough for most problems.

We now know that there are two elementary particles that are charged: protons and electrons. Electrons are negatively charged, while protons are positively charged. However, both have the SAME magnitude of charge: 1.6 x 10-19 C.

How Do Objects Become Charged?

So, if both protons and electrons are charged, can they both carry charge from one object to another?

Protons, which are much more massive than electrons, are tightly bound within the nucleus of each atom, so they are NOT free to move around. Even though they are charged, individual protons do not move from one object to another.

Electrons, however, exist in a cloud surrounding the nucleus, so it is much easier to remove an electron from an atom and transfer it to another object. Therefore, electrons are the elementary particles that move and carry charge from object to object.

Protons are held very tightly together in the nucleus of each atom, while electrons are free to move around in the space surrounding the nucleus
model of an atom

Can any Object Have MORE Than the Elementary Charge?

Now that we know that electrons are the particles that carry charge and that each electron contains a fixed amount of charge, let's see if we can finally explain exactly what is happening to make your hair stand up.

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