When a ferromagnetic material goes through a hysteresis loop, its theremal energy is increased. Where does this energy come from?

When spring is compressed its potential energy ………..

The length of a spring is increased by 2.5 cm the elastic potential energy stored in the spring is U . If the length is increased by 5 cm its elastic potential energy become ……

Answer the following, giving reason:- (a) When light travels from a denser to a rarer medium, the speed increases. Does it mean that there is an increase in the energy carried by the waves ? (b) The Sun appears reddish at sunset and sunrise.

For increase in internal energy of a system is equal to the work done on the system. Which process does the system undergo ?