Static vs Current Electricity

Electricity comes in two main kinds: static and current. Static electricity is a build-up of charge in one place; it can give you a small shock when you touch a doorknob or make your hair stand on end after rubbing a balloon. Current electricity is charge flowing through a wire or other conductor; it is what powers all your devices. Although they sound different, both involve the same basic thing: electric charge. The difference is just whether the charge is staying put or moving.

• StaticBuilt-up chargeStays in one place
• CurrentFlowing chargeThrough wires or materials
• Static exampleHair after a balloon rubOr a doorknob shock
• Current exampleLight bulb glowingOr a phone charging
• LightningHuge static + sudden currentCombines both
• DiscoveredAncient Greeks600 BC, rubbing amber

Static electricity

Static electricity happens when one object has an excess of electrons (negative charge) and another has too few (positive charge). The opposite charges attract each other, but as long as no conducting path connects them, no current flows. The charge just sits there: hence "static".

Static charge usually builds up through rubbing: as two materials slide past each other, electrons jump from one to the other. The famous example is rubbing a balloon on wool. The balloon becomes negative; the wool becomes positive. Stick the balloon to a wall and it stays for hours.

Common static experiences

• Sock-on-carpet shock: walking across a carpet in socks rubs charge onto your body. Touch a metal handle and the charge flows out of you suddenly: a tiny spark and a sting.
• Hair standing up: after rubbing a balloon on your head, the hairs all carry the same charge and repel each other.
• Sweater crackling: pulling off a jumper in dry weather makes tiny sparks and sounds.
• Clinging clothes: clothes fresh from the tumble dryer often have small static charges that make them cling together.
• Crisps bag: pulling apart a foil bag often produces a slight crackle and faint glow in the dark.
• Petrol pumps: at petrol stations, signs warn you to touch metal first because static from your clothes could spark and ignite petrol vapour.

Lightning is static electricity

The biggest example of static electricity in nature is lightning. Inside a thundercloud, water droplets, ice and hailstones tumble around in violent updraughts. The collisions transfer electrons. Generally the cloud builds up large negative charges at its base, while positive charges build up at the top of the cloud and on the ground below.

When the charge becomes huge enough (millions of volts), the air can no longer insulate. A sudden electrical discharge tears through the air: a lightning bolt. The bolt carries huge current for a fraction of a second, heating the air to over 30,000 degrees Celsius (5 times hotter than the surface of the Sun). The hot air expands explosively, producing the sound we call thunder.

Fact A single lightning bolt can carry over 30,000 amps of current and reach voltages of over 100 million volts. The whole bolt lasts only about 30 microseconds. About 1.4 billion lightning bolts strike Earth every year, killing around 24,000 people worldwide. In the UK, the chance of being struck is around 1 in 3 million per year.

Current electricity

Current electricity is charge in motion. Connect a battery to a wire and the battery pushes electrons through the wire. The flow of electrons is the current. Hook the wire to a bulb and the current heats the bulbs filament until it glows.

For current to flow, you need:

• A power source (battery, generator, solar cell) that provides voltage.
• A complete circuit: a path for the current to flow from one terminal of the source, through the load (bulb, motor, chip), and back to the other terminal. (See circuits.)
• Conductors: materials that let charge flow easily (metal wires).

How they relate

Static and current electricity are different states of the same thing: electric charge.

• Static: charge accumulated but not flowing.
• Current: charge flowing along a path.
• A static discharge (like a doorknob spark) is briefly a current flowing through the air or your skin.
• A lightning bolt is static charge in the cloud suddenly becoming a huge current.

Did you know? Static electricity is more common in dry weather. In humid air, water molecules cling to surfaces and gently conduct charge away, preventing buildup. In a dry winter heated home, charges can build up to thousands of volts (giving you that surprise shock at the doorknob). One simple fix is to keep the air a bit humid using a small humidifier, or just by drying laundry indoors.

Why it matters

Both static and current electricity have practical uses:

• Static: photocopiers and laser printers use static charge to stick toner powder to paper. Industrial paint sprayers use static to make paint particles cling to metal car bodies. Air filters use static plates to attract dust.
• Current: every electrical and electronic device, every light, every motor, every computer.

Try this Rub a blown-up balloon on a wool jumper or your hair for 10 seconds. Then hold it against a wall: it sticks, because static charge attracts the wall surface. Try holding it near small bits of torn-up tissue paper: they jump up to the balloon. Try holding it near a small stream of running water from a tap: the water bends. All these are demonstrations of static electricity at work.

Deeper dive: Ben Franklin and the kite experiment

For thousands of years, lightning was a complete mystery. Most people believed it was thrown by the gods to punish humans. In 1752, the American polymath Benjamin Franklin ran one of the most famous (and dangerous) experiments in history to prove that lightning was just electricity.

Franklin reasoned that if lightning was electrical, then by flying a kite into a thundercloud he should be able to capture some of the charge and prove the connection. He attached a metal key to the kites string, and at the bottom of the string he tied a silk ribbon (which would not conduct electricity, keeping him safer).

On a stormy day in June 1752, Franklin and his son William flew the kite from a shed in Philadelphia. As the storm cloud passed overhead, the loose strands on the kite string began to stand up: charged by electricity from the cloud. Franklin (carefully holding only the dry silk ribbon) touched the key and got a small electric shock and a spark.

His experiment was the first direct proof that lightning was electrical. (Note: a few years later, a Russian scientist trying to repeat the experiment was killed when he was struck by lightning. Do NOT try this at home.)

Franklin used his discovery to invent the lightning rod: a tall metal spike attached to the top of a building and connected by a thick wire to the ground. When lightning approaches, it discharges harmlessly through the rod and wire rather than through the building itself. Within decades, lightning rods were saving thousands of buildings (and lives) across Europe and America. They are still in use today, and the basic design has hardly changed.

Franklins work earned him membership of the Royal Society in London and worldwide fame. Today his face appears on the US 100-dollar bill, and he is remembered as one of the founders of the modern science of electricity.

For more, see circuits and conductors and insulators.