Question

why does the cord of an electric heater not glow while the heating element does?

Answer 1

The heating element of the heater is made up of alloy which has very high resistance. So, when current flows through the heating element,it becomes too hot and glows red due to heating effect of current. But the resistance of cord which is usually of copper or aluminium is very low so it does not glow.
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Answer 2

becoz heater have high resistance as compared to other heating elements. that's why due to high resistance as we increase current then more heat is produced. and the cord of heater is made up from alloy and other heating devices like bulb etc metals are used their resistivity is lower than alloy...