Sudeep and Karthideyan were room mates. Sudeep was boiling water in a vessel for bathing purpose. Karthikeyan said Sudeep , you know when you touch the middle part of the vessel containing water you can feel less heat than what you can feel at the top. Sudeep was shocked to hear. Karthikeyan took a thermometer and kept it at the top surface of water. The temepature was rising .Again he inserted it deep into the vessel containing water , now the temperature has fallen down than in the previous condition .What is teh truth behind it ?
(i) It is good to keep our hand deep into the vessel to check this while the liquid is boiling ? ,
(ii)What are convection current ?

Explanation

The truth behind this magic is convection process. It is a phenomenon of heat transfer in a fluid with the actual movement of the particles of the flud .i.e., when a fluid is heated the hot part expands and becomes less dense , so it rises up and replaces the colder part of fluid . Again this fluid is heated rises up of replaces the colder part of the fluid . This process goes on . That is why when we boil water heat will be from top layer of the liquid to the bottom layer.
(i) No, it is not good to check like this.As the top layer of fluid is not ,our hands must cross this layer first to move it deep into the veseel containing watter .so you may get burns or swells.
(ii) Convection currents are the constant cyclical motion of air water and other substance to distribute heat . As heated air rises ,for example it pulls cooler air into its place where it can be heated rise and pull in most coll air . Some geologists believe convection currents within the Earth's molten rocks (in semi-liquid state) are a contributing cause of volcanoes eqrthquakes and continental drift.