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Which of the following are the properties of a good heating element? I) It should have low resistivity. II) It should have high melting point. III) It should have low temperature coefficient of resistance. IV) It should have high specific heat capacity.
I, II and III
I, II and IV
Only II and III
II, III and IV
Only II and III
A good heating element requires high resistivity to generate sufficient heat through Joule heating and a high melting point to prevent it from burning out at operating temperatures. Additionally, a low temperature coefficient of resistance is necessary to ensure the power output remains stable as the element heats up.
A good heating element requires high resistivity to generate sufficient heat through Joule heating and a high melting point to prevent it from burning out at operating temperatures. Additionally, a low temperature coefficient of resistance is necessary to ensure the power output remains stable as the element heats up.
Think of a heating element like a filter in a water pipe: if the holes are tiny (high resistance), the water (current) struggles to get through, building up pressure (heat) behind it. You need the pipe material to be strong (high melting point) so it doesn't burst under that intense pressure.
HR-HM-LT (High Resistivity, High Melting-point, Low Temperature-coefficient).
H=I2Rt тАФ Joule's Law of Heating
R=╧БAlтАЛ тАФ Relation between resistance and resistivity
RtтАЛ=R0тАЛ(1+╬▒╬ФT) тАФ Temperature dependence of resistance
According to Joule's Law of Heating, the heat produced in a conductor is given by H=I2Rt. A heating element must have high resistivity (and thus high resistance R) to maximize heat output for a given current I. It must maintain its structural integrity at very high temperatures, which requires a high melting point. A low temperature coefficient prevents the resistance from increasing drastically, which would otherwise reduce the current and power output as the device gets hot.
High resistivity ensures high heat generation for a given current.
High melting point prevents oxidation and fusion at high temperatures.
Low temperature coefficient ensures stable resistance over a wide range of operating temperatures.
Heating elements are typically made of alloys like Nichrome (Ni-Cr) due to these desirable properties.
Efficient conversion of electrical energy into thermal energy.
Long operational life due to alloy stability.
Resistance increases slightly with temperature, leading to a small drop in current.
High thermal stress can lead to fatigue over long periods.
Electric iron
Room heaters and toasters
Nichrome (80% Nickel, 20% Chromium) is the industry standard for heating elements.
Option I is incorrect because low resistivity would result in very little heat generation (HтИЭR).
Option IV is incorrect because high specific heat capacity would make the device heat up very slowly, which is undesirable for a heating element.
C is correct тАФ A heating element must have high resistivity for heat production, a high melting point to withstand extreme heat, and a low temperature coefficient of resistance for stability.
Always remember that resistance is directly proportional to resistivity (RтИЭ╧Б); therefore, a heating element needs high ╧Б to produce high heat.
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