# A piece of copper and another of germanium are cooled from room temperature to 77 K, the resistance of a) Each of them increases b) Each of them decreases c) Copper decreases and germanium increases d) Copper increases and germanium decreases

## Question ID - 150865 :- A piece of copper and another of germanium are cooled from room temperature to 77 K, the resistance of a) Each of them increases b) Each of them decreases c) Copper decreases and germanium increases d) Copper increases and germanium decreases

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 (c) We know that resistance of conductor is directly proportional to temperature ( , ), while resistance of semiconductor is inversely proportional to temperature . Therefore, it is clear that resistance of conductor decreases with decrease in temperature of - while in case of semiconductor, resistance increase with decrease in temperature of - Since, copper is pure conductor and germanium is a semiconductor hence, due to decrease in temperature, resistance of conductor decreases while that of semiconductor increases.
 Neutral temperature of a thermocouple is defined as the temperature at which a) The thermo .m.f. changes sign b) The thermo .m.f. is maximum c) The thermo .m.f. is minimum d) The thermo .m.f. is zero 