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

The heating element has far more resistance than the conducting wire inside the cord. Also it's made into coil so that it offers more obstruction to the electric current flow. Hence the electric energy is converted into heat energy and temperature increases. The temperature increases so that the radiation has a wavelength that corresponds to red light.

Also this glow can only be observed when the heater is on and not immersed in water, so that heat energy rapidly increases the temperature of heating element and it glows.

Regards,

Team,

TopperLearning.