why does the conecting cord of electric heater not glow while the heating element does?
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A heating element is made of a high resistance material. It is made of a strong alloy of metals and other materials. It has a high resistance. So when current is passed through it, heat energy at power P = V²/R = I² R, is dissipated.
The resistance r of the conducting wire (connecting cord) is very low. So r << R. It is made of soft copper. The power dissipated through the wire is = I² r.
Current I passing through the connecting cord and the heating element is the same as they are in series.
So I² R >> I² r
So the heat dissipated in the heating element is very high. The heat dissipated in the cord is very less. It is almost negligible. So it does not get heated up quickly.
ΔT = Heat/(m s),
where m = mass, s = specific heat and ΔT is the increase in temperature.
So ΔT for the heating element is very high and for cord it is very less.
When the heating element heats up to very high temperatures, it radiates a lot of energy. It radiates red light in the visible spectrum, as the temperature crosses 2000 °C. (Principle of black body radiation).
As the temperature rise in the wire is very less, the radiation from the cord is not in the visible light range. So it does not glow.
The resistance r of the conducting wire (connecting cord) is very low. So r << R. It is made of soft copper. The power dissipated through the wire is = I² r.
Current I passing through the connecting cord and the heating element is the same as they are in series.
So I² R >> I² r
So the heat dissipated in the heating element is very high. The heat dissipated in the cord is very less. It is almost negligible. So it does not get heated up quickly.
ΔT = Heat/(m s),
where m = mass, s = specific heat and ΔT is the increase in temperature.
So ΔT for the heating element is very high and for cord it is very less.
When the heating element heats up to very high temperatures, it radiates a lot of energy. It radiates red light in the visible spectrum, as the temperature crosses 2000 °C. (Principle of black body radiation).
As the temperature rise in the wire is very less, the radiation from the cord is not in the visible light range. So it does not glow.
kvnmurty:
:-)
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because it has negligebel resistance
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