Electricity basics
What Is a Short Circuit?
- Grades 3-8
- 10 minute activity
- NGSS 4-PS3-2
Quick answer
A short circuit happens when electricity finds a shortcut: an easier path that skips the part it was supposed to power. Electricity takes the easiest path it can, so it rushes through the shortcut and the light, buzzer or motor stops working. In a play dough circuit, a short happens when the two pieces of dough touch.
Why is it called a short circuit?
A circuit is a loop that carries electricity from the power source, through a load like an LED, and back. A short circuit is a shorter loop that gets back to the power source without going through the load.
Electricity always takes the path of least resistance, the easiest way through. Think of a crowd leaving a stadium: if there is a wide-open shortcut, nearly everyone takes it. When the two pieces of dough touch, the dough itself becomes that easy shortcut, so almost no electricity goes through the LED and it goes dark.
Try it with dough
See a short circuit in play dough
You can make a short circuit, and fix it, in about a minute.
You need
- Battery holder with 4 AA batteries
- Conductive (salty) play dough
- White insulating dough
- 1 LED
Steps
- Build a simple circuit: two pieces of conductive dough with a gap, the red wire in one and the black wire in the other, and an LED across the gap.
- Switch on. The LED lights.
- Slowly push the two pieces of dough together until they touch. Watch the LED go dark.
- Pull them apart again and the LED comes back on.
- Now press a thin wall of white insulating dough between the two pieces and push them together. The LED stays lit.
What happens
When the dough touches, electricity skips the LED and takes the shortcut. The insulating dough blocks that shortcut, so electricity has to go back through the LED.
Not working?
LED still dark with the white dough in place? Make sure the white wall goes all the way through, so no conductive dough touches anywhere. And switch the battery holder off while you fix it.
How to fix a short circuit
Give the electricity a gap it cannot cross. Pull the two pieces of conductive dough apart, or press a wall of white insulating dough between them. Any insulator works between the pieces: an air gap, a piece of plastic, even paper.
White dough is handy because you can build with it. Use it anywhere two conductive pieces need to sit close together without touching, like the body and arms of a snowman.
Short circuits at home
The wiring in a house carries far more power than a battery pack. If a damaged cord or water lets electricity take a shortcut, a huge amount can rush through the wires at once. Wires can get very hot, spark or even start a fire.
That is why homes have fuses and circuit breakers. When too much electricity flows, a fuse melts or a breaker clicks off and cuts the power before the wires overheat.
Luckily, Squishy Circuits battery holders have built-in protection too: a resettable fuse that shuts off when it senses a short circuit, so a short in your dough is not dangerous. It is still important to learn about short circuits and how to prevent them.
Short circuit safety
Do
- Keep a gap between pieces of conductive dough
- Use white insulating dough when pieces need to sit close together
- Switch the battery holder off when you are done
- Tell an adult about damaged cords or plugs at home
Don't
- Let two pieces of conductive dough touch
- Touch the metal tips of the red and black wires together
- Leave a shorted circuit switched on
- Ever experiment with wall outlets or household wiring
Key words
- Short circuit
- A shortcut that lets electricity skip the load and go straight back to the power source.
- Path of least resistance
- The easiest path through a circuit. Electricity mostly takes this path.
- Resistance
- How much a material or part pushes back against electricity.
- Load
- The part that uses the energy, like an LED, buzzer or motor.
- Insulating dough
- Dough made with sugar instead of salt. It blocks electricity.
- Fuse and circuit breaker
- Safety parts at home that cut the power when too much electricity flows.
Watch: what is a short circuit?
Short circuit questions
What does short circuit mean?
A short circuit is when electricity takes a shortcut that skips the part it was supposed to power and goes straight back to the power source. The load stops working, and in household wiring a short can be dangerous.
What causes a short circuit?
Anything that gives electricity an easier path than the one through the load. In a dough circuit, it is usually two pieces of conductive dough touching. At home, it can be damaged wires, loose connections or water.
Is a short circuit dangerous?
In household wiring, yes. A short can make wires hot enough to cause a fire, which is why homes have fuses and breakers. A Squishy Circuits battery holder runs on low voltage and has a built-in resettable fuse that shuts off during a short, so a short in your dough is not dangerous. Still, switch it off and fix the short when you find one.
What is the difference between a short circuit and an open circuit?
An open circuit has a break in the loop, so no electricity flows at all. A short circuit has an extra shortcut, so electricity flows but skips the load. Either way, the LED goes dark.
Why does the LED turn off when the dough touches?
When the dough touches, the dough becomes a much easier path than the LED. Nearly all of the electricity takes the shortcut, so not enough goes through the LED to light it.
How do you fix a short circuit in play dough?
Pull the pieces of conductive dough apart so there is a gap, or put white insulating dough between them. The insulating dough lets you build pieces right next to each other without a short.
Printable guide: Circuits Explained (PDF)
Next, try a project
Build the light-up Snowman It uses white insulating dough to keep the circuit from shorting.