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Which alloy is commonly used for making electrical resistance wires such as heating elements in domestic appliances?
Brass
Bronze
Nichrome
Solder
Nichrome
Nichrome, an alloy primarily composed of nickel (80%) and chromium (20%), is used for heating elements due to its high electrical resistivity and high melting point. It does not readily oxidize or burn out even when heated to high temperatures in the presence of air.
Nichrome, an alloy primarily composed of nickel (80%) and chromium (20%), is used for heating elements due to its high electrical resistivity and high melting point. It does not readily oxidize or burn out even when heated to high temperatures in the presence of air.
Think of Nichrome like a narrow, busy hallway in a school; because it is harder to 'walk' through (high resistance), the students (electrons) bump into the walls, creating friction and heat, just like a heater element.
N-C: Nickel-Chromium heats the Room.
H=I2Rt тАФ Joule's law of heating where H is heat, I is current, R is resistance, and t is time.
R=╧БAlтАЛ тАФ Resistance formula where ╧Б is resistivity, l is length, and A is cross-sectional area.
The principle is based on Joule heating, where electrical energy is converted into thermal energy as current flows through a high-resistance material. According to H=I2Rt, a higher resistance (R) directly increases the heat (H) produced for a given current (I). Nichrome's ability to form an adherent layer of chromium oxide prevents further oxidation, allowing it to withstand repeated heating cycles.
Nichrome has a very high melting point, typically around 1400┬░C.
It exhibits excellent resistance to oxidation at high temperatures.
It remains chemically stable when exposed to oxygen, forming a protective surface layer.
High electrical resistance
High melting point
High resistance to corrosion and oxidation
Relatively expensive compared to iron-based alloys
Brittle after prolonged use at high temperatures
Electric toasters and irons
Hair dryers and space heaters
Resistivity of Nichrome is approximately 1.0 to 1.5 ╬╝╬йтЛЕm.
Option A (Brass) is an alloy of copper and zinc, which is conductive but not ideal for heating elements due to lower melting points. Option B (Bronze) is an alloy of copper and tin. Option D (Solder) is an alloy of lead and tin with a very low melting point, used for joining electrical components.
C is correct тАФ Nichrome is chosen for heating elements because of its high resistance and high melting point, allowing efficient conversion of electricity to heat without melting or oxidizing.
Always remember that materials for heating elements must have a high resistivity (to produce heat) and a high melting point (to avoid melting during use).
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