eli5: Why is there a tiny spark sometimes when plugging into an outlet?
In: Physics
Voltage is a difference in electrical potential between two entities. The two sides of an (AC) outlet are always in a state of difference in voltage, meaning there is always a difference in potential between them. Electric potential always “wants” to be the same. So when presented with a conductive path, that electric potential will equalize. When you add resistance to the path, you get current flow. That is what the windings in a motor, or the filament in a lightbulb do. In the case of the light, the resistance provided by the filament in the light bulb, causes it to heat up and emit light. When you approach a socket with a plug of a device that is off, the resistance within the device is too great for any current to flow, and you get no spark. When you approach the socket with the plug of a device that is on, there is a path within the device for current to flow, and it will flow as soon as the path is made.
Now the path, and the spark… The air around our light sockets and what we breathe is not nothing. It is a mix of gasses, and airborne solids. Electric current will flow through this air when the resistance is low enough, and/or the electrical potential is great enough. As you approach a socket with the plug, the resistance to current flow between the two becomes less and less as the air gap becomes smaller (and thus the resistance to current flow). Right before you have contact, the difference in potential between the plug and the energized outlet overcomes the resistance in the air gap. Just like a light bulb, when you pass enough current through the resistance in the air, it will heat up the electrons of the gasses and solids in the air and emit light, or “spark”. It really is the same as lightning in principal. The main difference is that the difference in potential is far far greater in a storm, as the charged energetic mass of a storm cloud, gets higher and higher (due to turbulent friction of the molecules in the cloud) compared to the “ground” of earth. Eventually, the resistance of the atmosphere is overcome, and the potential difference between the cloud and earth is momentarily equalized via the violent arc we know as lightning. That little click you might hear when the spark is made at the outlet, is baby thunder.
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