Why do the bubbles get bigger and bigger when water boils?

When cold water is just heated, the bubbles become smaller and smaller as they rise, because at this time the bubbles are dissolved air in the water. Since it has just been heated, the convection of the water is not obvious yet, that is, the lower water temperature is higher. , the temperature above is lower, so due to the principle of thermal expansion and contraction, the bubbles become smaller and smaller as they rise.

After water boils, the bubbles become larger and larger as they rise, because at this time the bubbles contain a large amount of water vapor produced by boiling water. When boiling, convection has basically stopped, the water temperature above and below is basically the same, and there is no heat. The problem of expansion and contraction, but because the pressure of water increases with the depth, the higher the bubble reaches the top, the smaller the pressure of the water it receives. In this way, the internal and external air pressure is unbalanced, and the internal air pressure is greater than the external air pressure, so the bubbles will expand and become It is so large that it breaks open when it reaches the water surface, and the water vapor inside is emitted into the air.