Why does the plug glow when it enters the socket?

The reason for the occurrence of arcs is the presence of air between conductors, and when the two conductors come into contact, heat is released (the thermal effect of electric current), and if there is air between them, an arc is triggered. This arc will be small when the two conductors are in full contact until there is no longer an air gap between them, in other words, the greater the heat released when they come into contact (the greater the current), or the larger the air gap, the larger the arc.

Because the electrical switch is on, when the plug enters the socket, the electrical appliance will run, and the operation will produce a current loop, so it is normal to have electric light.

High-energy states are usually unstable and will spontaneously transition to low-energy states. Just as a stone at the top of a mountain can easily fall to the bottom of a mountain.

As the electricity ionizes in the air and breaks through the air, an electric arc is created and the electricity flows continuously in the arc.

When the plug is in the socket, the appliance runs.

This proves that the socket is about to break down and it's time to change it.

This may be the cause of an electric arc.

The voltage in the socket is alternating current, assuming that the voltage of the plug that is not connected in the hand is the same as the earth, then the two holes on the left and the right side of the socket hole will produce a voltage difference of 0-220V with the plug in the hand, and the jack in the middle is the same as the voltage in our hands because it is the ground wire. So electric sparks can only appear in the jacks on the left and right sides of the AC triature jack.

Based on the definition of the electric field strength just now, we calculated that the distance required to break through the air is 0-73 microns. 73 microns (millimeters), which is slightly smaller than millimeters and almost indistinguishable on the scale, but the distance at which breakdown occurs in real life is much higher than 73 microns, and may even be a few millimeters.

Air is mainly composed of nitrogen and oxygen, both of which are very stable gases at common temperatures, do not decompose, and do not ionize. However, if there is an electric field in a defined region, and the electric field is strong enough, the electrons in oxygen and nitrogen will break away from the nucleus under the action of the electric field and flow in the direction of higher voltage, which is ionization.

If the field is strong, a large number of electrons break free from the shackles and run out in one direction, and the air that is not conductive will form a conductive pathway, which is the electric field breaking through the air. Note that the spark has not yet appeared at this time.

In the presence of a strong electric field, the electrons not only absorb the energy of the electron volts and break free from the restraints, but also are accelerated to hit other oxygen molecules in flight, and the electrons around the oxygen and nitrogen molecules that were originally running stably are also knocked out, so that a large number of electrons begin to move in the same direction. A path that can conduct electricity is formed. Note that the spark has not yet appeared at this time.

When the electrical appliance connected to the plug is turned on, the plug will be plugged in. This is the phenomenon when the current is turned on to form a loop, which is actually the arc that occurs at the moment of line contact, which is similar to lightning in rainy weather, which is the same physical phenomenon.

Sparks (electric light) when plugged in are caused by poor contact, usually when the hand shakes when plugged in.

It can be avoided by:

Turn off the electrical appliances before plugging them in, plug them in and turn them on again.

Or use an outlet with a switch, plug in the appliance, and then turn on the switch on the outlet.