Question

For which of the following the resistance decreases on increasing the temperature.
A. Copper
B. Tungsten
C. Germanium
D. Aluminium

Answer 1

Hint: Here we have to find the relation between the resistance and temperature how they both depend on each other in case of conductors as well as semiconductors. As in given options, three options are conductors that are Copper, Tungsten and Aluminums and one option is semiconductor that is Germanium.

Complete step by step solution:
First check for conductors: Conductors contain free electrons that help in conduction of electricity. When the temperature of the conductor rises, atoms start vibrating more frequently which causes an increase in the number of collisions of atoms. Therefore, this increases resistance to the movement of electrons present in the atoms which are colliding.

Now, for semiconductors: It contains electrons in the valence band as well as in the conduction band. Only a small amount of energy is needed to move the free electrons from valence band to conduction band. When the temperature of a semiconductor rises, free electrons move from valence band to conduction band and hence there will be less collision and more free movement. Therefore, the resistance decreases with increase in temperature in case of semiconductors. The only semiconductor in given options is option C that is germanium.

 Hence, the correct answer is option C.

Note: We need to identify from the given options which are the conductors and which one is semiconductor in order to get the right answer. Only in case of semiconductors the resistance decreases with increase in temperature as the atoms are in excited state to move from valence band to conduction band.