Question

An alloy used in making heating elements for electric heating device is :
A. Solder
B. Alloy steel
C. Nichrome
D. German silver

Answer 1

Hint: We know that alloy is a combination of more than two metals. And heating elements should have a high melting point so that high temperature may be obtained. It should not oxidise at high temperature and should have high resistance. The required alloy for us in this question is also used in hair dryers.

Step by step solution:
Alloying improves the properties of metals often by making them stronger and more corrosion resistant. For example Bronze (copper and tin), is used to make bells, hammers and wrenches.
Alloys are used in electrical heating devices rather than pure metals because the resistivity of an alloy is more than the resistivity of a pure metal. Alloys do not burn easily even at high temperatures.
An alloy of nickel and chromium (80%nickel, 20% chromium) is used in making heating elements for electric heating devices is nichrome. It is used as a resistance wire.
Nichrome 80/20 is an ideal material, because it has relatively high resistance and forms an adherent layer of chromium oxide when it is heated for the first time.
Nichrome does not burn easily at high temperature i.e. it has a higher melting and boiling point than metals. Therefore it will resist the flow of charges more and lead to development of heat faster.
Solder is not used because it has a low melting range. It is made of tin and lead.
Alloy steels are made of iron, carbon and other elements such as vanadium, silicon, nickel etc. And it is high temperature resistance and corrosive.
German silver is an alloy of copper, zinc and nickel. It has high electrical resistance, so it is used in heating coils. Its cost is higher than the nichrome.
So, the conclusion from the above points is that the effective alloy for making heating elements for electric heating devices is Nichrome.
So, the correct answer is “C”.

Note: Nichrome is also a good conductor. The working of heating elements is based on the heating effect of electric current. When a current passes through a resistance, it produces the heat.