Correct Answer - Option 4 : Aluminium decreases and silicon increases
CONCEPT:
Electrical Resistance:
- The measurement of the opposition of the flow of electric current through a cross-section of the material is called the electrical resistance of that material.
- It is denoted by R.
- The relationship between resistance and temperature is given by:
⇒ R = R0 (1 + α Δ T)
Where R0 is resistance at a reference temperature, α is temperature-coefficient of a conductor, and Δ T changes in temperature.
EXPLANATION:
Variation of resistance with temperature:
- In metals, the current flow due to electrons. As the temperature increases, the random motion of the free electron also increases.
- The increase in random motion of free electrons increases the resistivity of the metals. Therefore the resistance of the metal increases as the temperature increases.
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Semiconductors like Silicon and Germanium contains lesser charges than those of metals but has more charges than insulators. These charge carriers are generated by the thermal breaking of bonds.
- Thus, as the temperature rises, more covalent bonds break, releasing more electrons and the number of electrons and holes will increase which lowers the resistivity rapidly. Therefore the resistance of semiconductors decreases with increasing temperature.
- The resistance of metal decreases as the temperature decreases. So the resistance of the aluminum will decrease when it is cooled.
- The resistance of semiconductors increases as the temperature decreases. So the resistance of the silicon will increase when it is cooled.
- Hence, option 4 is correct.
