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Q54
(NDA-II/2023)
Science & Technology › Basic Science (Physics, Chemistry, Biology)
Official Key
The heating element in an electric iron is usually made of
Explanation
The heating element in an electric iron is made of Nichrome, which is an alloy typically consisting of 80% Nickel and 20% Chromium. It is chosen for heating applications due to several critical properties:
- High Resistivity: Nichrome has high electrical resistance, which enables it to efficiently convert electrical energy into heat energy through Joule heating (H = I²Rt).
- High Melting Point: It has a high melting point (approximately 1400°C), allowing it to withstand the high temperatures required for ironing without melting.
- Resistance to Oxidation: When heated to high temperatures in the air, Nichrome forms an outer layer of chromium oxide. This layer is thermodynamically stable and protects the rest of the element from further oxidation or burning.
In comparison, Tungsten is used in incandescent bulbs because of its extremely high melting point but requires a vacuum to prevent oxidation, while Copper is a conductor with very low resistance, making it unsuitable for heat generation.
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