NCERT Solution for Class 10 Science Chapter 12
Electricity
NCERT Books for Session 2022-2023
CBSE Board and UP Board
Intext Questions
Page No-209
Questions No-4
Why are coils of electric toasters and electric irons made of an alloy rather than a pure metal?
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The resistivity of an alloy is higher than the pure metal and it does not corrode easily. Moreover, even at high temperatures, the alloys do not melt readily. Hence, the coils of heating appliances such as electric toasters and electric irons are made of an alloy rather than a pure metal.
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The coils of electric toasters, electric irons and other heating devices are made of an alloy rather than a pure metal because
(i) the resistivity of an alloy is much higher than that of a pure metal, and
(ii) an alloy does not undergo oxidation (or burn) easily even at high temperature, when it is red hot.
Since, alloys have higher melting point than pure metal so coils of electric toasters and electric irons are made of an alloy rather than a pure metal to retain more heat without melting.
coils of electric toasters and electric irons are mode of an alloy (generally nichrome) due to the following two reasons:
(i) Resistivity of an alloy is generally higher than that of pure metals, hence for a given resistance we need a coil of lesser length.
(ii) At high temperatures, an alloy does not oxidise (burn) readily. Hence, coil of an alloy has longer life.
Coils of electric toasters and electric irons are often made of an alloy rather than a pure metal for several reasons:
1. Resistance and Heating Properties: Alloys can be designed to have specific electrical resistance and heating properties. The resistance of a material is a crucial factor in the operation of heating elements. Alloys can be engineered to provide the desired resistance, allowing the toaster or iron to generate the appropriate amount of heat for its intended purpose.
2. High Melting Point: Heating elements in toasters and irons can reach high temperatures during operation. Alloys are often chosen because they can have higher melting points than pure metals, ensuring that the heating element remains stable and doesn’t melt or deform under the high temperatures.
3. Durability and Mechanical Strength: Alloys are often more durable and mechanically robust than pure metals. The mechanical strength of the heating element is important to withstand repeated heating and cooling cycles and mechanical stresses.
4. Corrosion Resistance: Alloys can be formulated to be more resistant to corrosion than pure metals. This is important in appliances like toasters and irons that may be exposed to moisture or humidity during use.
5. Cost-effectiveness: Alloys can be designed to provide the necessary properties at a lower cost than using a pure metal with similar characteristics. This consideration is often important in the manufacturing of appliances where cost efficiency is a significant factor.
One common alloy used for heating elements in appliances is nichrome, which is a nickel-chromium alloy. Nichrome has a high melting point, good electrical resistance, and is corrosion-resistant, making it well-suited for heating applications in electric toasters, irons, and other similar devices.