Choose the correct alternative:
(a) Alloys of metals usually have (greater/less) resistivity than that of their constituent metals.
(b) Alloys usually have much (lower/higher) temperature coefficients of resistance than pure metals.
(c) The resistivity of the alloy manganin is nearly independent of/ increases rapidly with increase of temperature.
(d) The resistivity of a typical insulator (e.g., amber) is greater than that of a metal by a factor of the order of (1022/1023).
(a) Alloys of metals usually have greater resistivity than that of their constituent metals.
Alloys are the homogeneous mixture of two or more metals and due to which alloys have better conducting properties as compared to pure metals. Pure metals have large number of free electrons and simple atomic arrangement but in alloys these free electrons number as well as their atomic arrangement changes. Hence alloys have greater resistivity than metals.
(b) Alloys usually have lower temperature coefficient of resistance than pure metals.
The resistance change factor per °C of temp change is called the temperature coefficient. Coefficient approaching zero can be obtained by alloying certain metals. So we can say that alloys have lower temperature coefficient of resistance than pure metals.
(c) The resistivity of alloy, manganin, is nearly independent of increase of temperature.
The resistivity of alloys is high and atoms are not arranged in proper order and with the increase in temperature resistivity increases due to collision and random motion of atoms.
(d) The resistivity of a typical insulator is greater than that of a metal by a factor of order of 1022.
In case of insulator, resistivity decreases with increase of temperature.