Question

Why are the coils of electric toasters and electric irons made of an alloy rather than the pure metal?

Answer 1

Hint:The alloy is the metal made by mixing two different metals to reach the desired requirements. Recall Joule’s law of heating, phenomenon of creep, melting point and oxidation to answer this question.

Complete answer:
To answer this question, we first need to understand the meaning an alloy. The alloy is the metal made by mixing two different metals to reach the desired requirements. We know that according to Joule’s law of heating: the heat produced in the metallic wire when the current flows through it is proportional to the resistance of the wire.

The coils of electric toasters and electric irons are made of an alloy rather than the pure metal because no pure metal meets the requirements of these wires used in electric irons and electric toasters. We know that pure metals have relatively low resistance. But the wires used in the electric toasters and electric irons should be such that they heat up as quickly as possible. Since the heat produced in the wire is proportional to the resistance, the resistance of the wire must be high. The wires made up of an alloy have relatively higher resistance than the pure metal and hence they are preferred over pure metal wires.
We know that most of the pure metals have relatively low melting point as compared to their alloys. Therefore, as the temperature exceeds a certain value, they start melting. Thus, the wires made up of an alloy are preferred because of their high melting point.
We know the phenomenon of creep. It is the deformation produced in the wires due to high temperature. The wires used in the electric toasters and electric motors resist the creep. Also, these wires resist the oxidation of metal at high temperature and do not burn up.

Note:To answer this question, students must know the definition of resistivity, melting point, oxidation and creep. Remember, the alloy made up of Nickel and Chromium known as Nichrome is generally used in such electric devices. According to Joule’s law heating, the heat produced in the metallic wire is also proportional to the time. Therefore, in more time, the heat produced will be more.