Electric charge is all around you, but you only really notice it on rare occasions, like when your hair stands on end after you take off a hat or when you get a sharp zap when you reach out to touch something after rubbing your feet along the carpet.
These two phenomena are examples of static electricity, something you probably learned about when you were a kid. But how does static charge make your hair stand on end and why can it give you a static shock?
What’s actually going on at the atomic level that produces these universal experiences? Learning the details about static electricity gives you a much more detailed insight into this fascinating property of matter.
The Basics of Electric Charge
Electric charge is a fundamental property of matter. It is separated into positive charges and negative charges, and although some particles are electrically neutral – such as the neutron – these are actually composed of even more fundamental particles which do carry an electric charge.
The two most important charged particles to know about when you learn about static electricity are two of the main components of an atom: protons and electrons.
Protons are positively charged, with a charge of +e, while electrons are negatively charged at –e, where e = 1.602 × 10−19 C. The C here stands for coulombs, which is the SI unit for electric charge. The 10−19 tells you that charged particles have very small charge values compared to one coulomb – two charges of just 1 C separated by a meter would generate a force bigger than the thrust of the Saturn V rocket’s launch thrust!
The fundamental rule for how electric charge works is that opposite charges attract and like charges repel. So if you brought an electron near another electron, they would push themselves apart, whereas if you brought an electron near a proton, it would be attracted to it.
Definition of Static Electricity
At the most basic level, static electricity simply refers to charges that aren’t moving. However, there is much more to it than that! The key thing about static electricity is that it occurs when there is an imbalance of charge, and this imbalance essentially creates electrical potential, meaning that there is the potential for electrical current to flow (to rebalance the charge) because of the positions of charge-carrying particles.
In atoms, and by extension most everyday objects, there is a balance between the positive and negative charges (i.e. between the protons and electrons), so they are electrically neutral when considered all together.
So if you brought one atom close to another, there would be no electrical force between them because all of the positive charges are balanced out by negative charges, so there is no net charge to generate a force.
While it’s really a little bit more complicated than this (because electrons always move, so they don’t always block the positive charge from the protons), this neutral situation creates a clear contrast with what happens when there’s a build up of static charge.
In essence, when an object (like your hair after rubbing a balloon on it) gains an excess or a deficit of charge (so more or fewer electrons than in its ordinary state), then it is no longer neutral and can generate what you call static electricity. In contrast, ordinary electricity is a continuous movement of charge (in the form of electrons in an electric current), while static electricity doesn’t involve movement until the charges rebalance each other – and possibly give you a sharp zap in the process!
How Static Electricity Works
Static electricity fundamentally depends on an imbalance between positive charges and negative charges, but really it’s only the electrons that actually move to create this imbalance.
In an atom, the protons are tightly-bound up in the nucleus (along with the neutrons), and both of these are considerably heavier than the negatively-charged electrons that stay in a “cloud” around the outside of the nucleus.
Because these lighter particles are on the outside, when one object makes contact with another it’s the electrons that can transfer between them, and rubbing them together increases the rate of charge buildup. So if an object picks up extra electrons, it becomes negatively charged, whereas if it loses electrons it becomes positively charged.
Insulating materials hold a static charge well, whereas a good conductor will only maintain a static charge in certain situations. A conductor given extra electrons doesn’t hold a static charge because the electrons can flow freely throughout the material (which is the definition of a good conductor).
So any charge buildup dissipates too quickly to create noticeable static electricity, and it can transfer into other objects unless it’s completely insulated from the rest of the environment. Because current can’t flow in an insulator, the static build-up quickly creates a notable charge imbalance and thereby generates static electricity.
Because like charges repel, and opposite charges attract, when something has a static charge it will stick to oppositely charged items, and it can also sometimes polarize atoms in an otherwise neutral object and stick to it too – the way a balloon sticks to a wall after you rub it on your head.
If the charge buildup is big enough and a relatively high voltage is achieved between the two surfaces or objects, the charge can jump from one object to another. This is why you can get a zap from the static shock if you rub your feet across the floor and then touch a doorknob.
Examples of Static Electricity
There are many examples of static electricity that you’ll encounter in everyday life, even if you don’t necessarily think about the role that static charge plays in their operation.
One particularly common example is static cling in clothes, especially after using the drier, which keeps the ideal conditions for static electricity to develop, and also involves clothes rubbing against each other and potentially picking up extra electrons on the way. The static shock from clothes charged in this way tends to be quite small, but you definitely still notice it when you get one!
Photocopiers are a great example of how static electricity can be put to good use. The bright light that scans the document creates an electrical “shadow” of the image on a photoconductive (i.e. light-sensitive) belt, and as the belt rotates, it picks up negatively-charged toner particles because of static charge.
Underneath this, another belt brings a sheet of paper around, giving it a strong positive static charge in the process. When the negative charges from the toner meet the positive charges on the paper, the toner imprints itself onto the piece of paper, in the same pattern as the shadow picked up by the photoconductive belt.
Another example should take you back to a physics class at school: The Van de Graaff generator, and the classic demonstration where somebody touching the sphere has their hair stand on end. The generator works based on the movement of static electric charges, with a moving belt running up the length of the device and two metallic “combs” to control the static charge.
A positively-charged comb at the bottom (connected to a supply of electricity) draws electrons from the belt, leaving it with a net positive charge, and this charge is picked up by a comb at the top, which spreads it out to the big dome at the top. If you touch the dome during the charging process, individual strands of your hair pick up matching charges and repel each other, making it stand on end!
Benjamin Franklin’s Kite Experiment
Lightning bolts are a very dramatic demonstration of the power of static electricity, and Benjamin Franklin proved this in one of the most well-known scientific demonstrations of all time by tying a key to a wet kite string during a thunderstorm.
While it’s a myth that the kite was actually struck by a lightning bolt (this would have likely killed Franklin), the electric field from the storm was picked up by the string, which – much like the classic Van de Graaff generator demonstration – made the strands of the twine stand on end. Finally, Franklin touched the key and felt the zap of a static shock, clearly demonstrating the link between electricity and lightning.
Of course, scientists have filled in many more details about the process since the days of Benjamin Franklin. Much like clothes rubbing against each other in the dryer or a balloon rubbing against your hair, the static charge that creates lightning comes from friction, and from ice crystals in cold air meeting water droplets from a warm air mass.
Charge builds up in different places in the cloud, and when there is a sufficiently high difference in electrical potential between these places (i.e. a sufficiently high voltage), it’s released in the form of a lightning bolt. This usually occurs within clouds or between two clouds, but occasionally the bolt will strike the ground.
The Triboelectric Series
The build up of static charge caused by friction and rubbing is technically called the triboelectric effect, and based on this article you already know the details of what causes this and how it works. Objects coming into contact with each other leads to one of them picking up extra electrons (all carrying negative charges) and the other developing a deficit of electrons and therefore a positive net charge.
However, the degree to which different materials pick up negative charge or lose electrons and gain a positive charge varies based on the characteristics of the material. While insulators are generally better at picking up static charge, different insulators pick it up at different rates.
For example, most types of rubber, and in particular Teflon, pick up electrons very easily and as such are great for demonstrations and pieces of technology dependent on static electricity. Materials differ based on their “electronegativity,” which basically means their electron affinity, or their tendency to pick them up from other objects.
The triboelectric series puts different materials into order based on their ability to pick up a positive or a negative static charge. Items placed toward the top of the triboelectric series are prone to picking up a positive charge, while those at the bottom are more likely to gain electrons and pick up a negative charge as a result. The greater the separation between two items in the triboelectric series, the more that rubbing them together will create a static charge in both of them.
The Dangers of Static Electricity
While most of the demonstrations of static electricity are fun displays or minor curiosities that you encounter in day-to-day life, it’s important to remember that unwanted static charge can have serious consequences.
For example, a single spark from static electricity can ignite flammable liquids or gases and potentially result in an explosion. The static build-up from sliding across your car seat could even potentially cause a problem when it comes to refilling your gas, and so you should always touch the metal part of the car before filling up.
Of course, most of the time static electricity really is just an interesting phenomenon, but understanding how it works can help you avoid catastrophe in some situations.
- NASA (Wayback Machine): What Was the Saturn V?
- Explain That Stuff: Static Electricity
- Science Made Simple: What is Static Electricity?
- Science ABC: Why Does Static Charge Build Up?
- Live Science: What Is Static Electricity?
- BBC GCSE Bitesize: Static Electricity
- Library of Congress: How Does Static Electricity Work?
- All About Circuits: Static Electricity
- Science ABC: How Does A Photocopier Work?
- S-Cool: Conductors and Insulators
- Alpha Lab: Common Static Electricity Problems and Remedies: A Series of Brief Articles
- NASA: How Is Lightning Made?
- Georgia State University Hyper Physics: Van de Graaff Generator
- The Franklin Institute: Benjamin Franklin and the Kite Experiment
- Harvard University: Triboelectric Series