Question

A PIECE OF COPPER AND ANOTHER OF GERMANIUM ARE COOLED FROM ROOM TEMPERATURE TO 77K, WHAT HAPPENS TO THEIR RESISTANCES OF EACH

Answer 1

Resistance of copper increase because it is a high conductive metal & resistance of germanium increase due to it is semiconductor metal

Answer 2

First of all we know metals have good number of mobile electrons as compared to the semiconductor like germanium…So when we heat a metal the kinetic energy of electrons increases so their will be a great rush between the electrons (comparing to the situation that when will be your running speed more in the market with atmost crowd or in a playground while playing football??) So the speed of electrons decreases and the conductivity decreases i.e, resistance increased. Opposite is the case with the semiconductor they have balanced no.of electrons so when you heat a semiconductor the electrons get accelerated i.e, the bond breaks and electrons get freedom to move (not all) so resistance decreases and conductivity increases. Now whatever i have said above was for increasing the temperature but the question was for cooling so now you can reverse the situation that metal electrons get settle, rush decreases so conductivity of metal increases i.e, resistance of copper decreases…..While the electrons of semiconductor gets settle too but they get bonded and less electrons can move to the conduction band so conductivity of semiconductor decreases i.e, resistance of germanium increases.

Conclusion:-Resistance of Copper decreases and resistance of germanium increases…