Question

The resistivity of an alloy is ${R_{alloy}}$ . The resistivity of the constituent metal is ${R_{metal}}$. Then usually, the:
A) ${R_{alloy}} > {R_{metal}}$
B) ${R_{alloy}} = {R_{metal}}$
C) ${R_{alloy}} < {R_{metal}}$
D) There is no relation between ${R_{alloy}}$ and${R_{metal}}$.

Answer 1

To answer this question we should understand what an alloy is and how it is different from metal. Also, we should try to understand the changes in metal when an alloy is formed. The properties of a metal and an alloy should also be considered important to answer this question.

Complete answer:
The resistivity of any substance can be defined as the electrical resistance of a conductor of a unit cross-sectional area and a unit length. Every material has some amount of resistivity. Some have high resistivity and some have low resistivity. More the resistivity, less is the amount of current carrying capacity by the material and lesser the resistivity more is the current carrying capacity of the material. Higher resistivity substances are insulators and lower resistivity material are conductors.
Metals are generally considered good conductors. They allow current to flow through them easily because of the free electrons present in their outer shell. We convert metals into alloys by adding some other metal and/or nonmetals to get better properties. Most of the time non-metals are added.

The non-metals are poor conductors of electricity. Also, the crystal structure of non-metals is different from that of metals. When we add non-metals to metal, the crystal structure changes which decreases their ability to conduct electricity. Thus increasing the resistance and hence resistivity.
So we can say that the resistivity of the alloy is greater than the resistivity of the metal. So${R_{alloy}} > {R_{metal}}$.

Thus option (A) is the correct answer.

Note: The unit of resistance is the ohm ($\Omega$).The value of resistivity depends on the temperature of the material. The resistivity of metallic conductors generally increases with a rise in temperature. But resistivity of semiconductors, such as carbon and silicon, generally decreases with rise in temperature.