Question

Alloys are commonly used in electrical heating devices like toaster, electric iron because:

• A. they oxidise readily at high temperature.
• B. they do not oxidise readily at high temperature.
• C. they are poor insulator of electricity.
• D. they have low resistivity.

Hint:

An ideal heating element requires:
1. High resistivity (to produce more heat per unit length).
2. High melting point.
3. High resistance to oxidation at high temperatures.

Answer 1

The Correct Option is B

Step 1: Think about what a heating element must survive.
A heating coil in a toaster or iron glows red hot every time it is used, so whatever it is made of must be able to handle repeated exposure to high temperature without falling apart.
Step 2: Compare pure metals with alloys.
Pure metals tend to react with oxygen in the air and oxidise or burn away quickly once they get very hot, which would wear out the element in no time.
Step 3: See why alloys solve this problem.
Alloys such as nichrome resist this oxidation at high temperature, along with having a high resistivity and high melting point, so they keep working reliably heat after heat without corroding or burning out.
\[ \boxed{\text{They do not oxidise readily at high temperature}} \]