Question

The filament of electric heater glows red hot whereas connecting wires don't . Explain.

Answer 1

This is because the filament of heater is made of material such as tungsten and tungsten provide resistance to flow of electricity converting it into heat energy

Answer 2

it is because electric heater contain resistor of high resistance, due to which temperature increases.
$h = {i}^{2} rt$
h is directly proportional to r