Question

What happens to metal balls when they are heated? What does this show?

Answer 1

Hint: In order to solve this question we need to understand heat. Heat is a form of energy which flows due to temperature difference. Heat propagates in space through three different methods, first is conduction, second is convection and third is radiation.Conduction is a form of heat transfer in which heat propagates by exchange of phonons, as when heated atoms vibrate and transfer their energy to neighboring atoms in the form of phonons. Convection is a form of heat transfer in which heat exchange by exchanging matter with surrounding, for example hot air rises in space. Radiation is a form of heat transfer in which heat energy exchange by photons transfers, for example blackbody radiation.

Complete answer:
A metal ball is made up of atoms having minimum interatomic distance, so when we heat the metal its atoms actually vibrate about their mean position and thus colliding with neighboring atoms and making them to vibrate, due to this continuation process metals size increases or metal expands on heating.

For example, railway lines made of iron (a metal) expands in a hot summer, so the gap between them increases. This shows that metals or any other solid objects when subjected to thermal energy gets expanded.Also the solid objects contract if temperature is decreased.

Experiment to prove it: Take a metal ball and pass it through a ring, suppose ring size is just greater than metal ball.Now take the metal ball and put the candle flame beneath it, so the metal ball gets heated, now pass the metal ball through that ring, you would find that metal balls stuck and do not get through the ring as its size increases.This proves that a metal ball expands on heating.

Note: It should be remembered that heat inside a metal ball or rod propagates through Conduction. As when a metal ball is heated then atoms vibrate and transfer their energy to neighboring atoms in exchange for phonons. However the heat radiated by the metal propagates in space by radiation, for example blackbody radiation.