how is physics applied in lighting a candle?

Answer 1

You hold a flame near, or direct it onto, the wax-laden upper end of the candle wick. Combined convective and radiative heat transfer melts then vaporizes the wax and the vapor ignites.
After ignition the flame continues through the mechanism of heat transfer from the candle flame to the wax-laden wick which keeps the flame alive, and heat transfer to the wax pool that forms at the top of the candle (where the wick emerges from the candle) which keeps the flame supplied with fuel.. Capillary action, a surface tension phenomenon, causes molten wax to climb the wick where it provides a continuous supply of new wax to burn.