Why does a candle extinguish itself after being covered with a glass?

Answer 1

The burning flame on a candle needs three things to continue burning:

1) fuel, which it gets from the wick

2) heat, which comes from lighting the candle

3) oxygen

Without any one or more of these three things, the candle will no longer continue to burn. In the case where a candle is covered with a glass, the candle quickly uses up the oxygen inside the glass. once all of the oxygen is gone, the flame will burn out.

Answer 2

When you cover a candle with a glass, it creates a limited supply of oxygen available for the flame to burn. As the flame consumes the oxygen inside the glass, it eventually uses up all the oxygen and goes out, extinguishing the flame.