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

$(a)$ State the commercial unit of electric energy and find its relation with its $SI$ unit.
$(b)$ The current through a resistor is made three times its initial value. Calculate how it will affect the heat produced in the resistor.
$(c)$ Find the increase in the amount of heat generated in a conductor if another conductor of double resistance is connected in the circuit,keeping all other factors unchanged.

$(a)$ Give reasons why tungsten is used for making the filament of electric lamps.
$(b)$ Why are the heating elements of electrical appliances made up of an alloy rather than a pure metal?

In an electrical circuit,three incandescent bulbs $A, B$ and $C$ of rating $40 \, W, 60 \, W$ and $100 \, W$ respectively are connected in parallel to an electric source. Which of the following is likely to happen regarding their brightness?

An electric lamp is marked $100 \, W, 220 \, V$. It is used for $5$ hours daily. Calculate: $(i)$ its resistance while glowing. $(ii)$ energy consumed in $kWh$ per day.

Give two practical applications of the heating effect of current.