When current is flowing through a heater coil it glows but the supply wiring does not glow because
A. current through supply line flow with a lower speed
B. supply wiring is covered with an insulating layer
C. Resistance of heater coil is more than supply wires
D. supply wires are made of superior material

Hint: Joule heating is the physical phenomena taking place by which the pass of current through an electrical conductor creates thermal energy. This thermal energy is then proved through a rise in temperature in the conductor material. Therefore t is known as heating.

Complete step-by-step answer:
Joules heating is a process happening when an electric current is passed through a high resistance wire, the resistance wire will become very hot and develop heat. This effect is called the heating effect of current or also known as Joule's law of heating. Nichrome is an example where joules heating is taking place.
$H={{I}^{2}}Rt$
Where $I$ is the current, $R$ is the resistance and $t$ is the time taken.
Joule’s law of heating is not considered to be a reversible process, since we could not directly develop electric current by just heating up any resistance. Therefore the Joule effect is not reversible. It is thermally irreversible in nature In an electrical heater, the supply wire is having very low resistance compared to heater coil, therefore according to Joules heating effect heat developed in the supply wire is very much less and hence it will not glow when current is flowing through it. Therefore the correct answer is given as option C.

Note: Electric heating is having so many advantages. Electric Heating is having assured safety and Reliability. Electric heating is the safest possible heating solution at our home with no burning materials, combustible gases, or noxious fumes. And also electric Heating can be affordable and efficient. It is environmentally friendly.