Deborah takes a candle and places it in a tub. She lights the candle and fills the tub with some water. Then she covers the candle with an inverted glass. What happens after some time?
Water rises in the inverted glass
In the question above a burning candle is kept in a tub and the candle is covered with an inverted glass. To burn, the candle needs a continuous supply of oxygen. When all the oxygen inside the glass is used up the candle stops burning.
The volume of the air decreases and the water rises. This is because the outside air pushes water into the container until the pressure inside the glass is equal to the pressure outside.