Why are alloys commonly used in electrical heating devices?

The $SI$ unit of electric charge is $.........$

Positive charges flow from high potential to low potential.

$(i)$ Name and state the law that gives the relationship between the current through a conductor and the potential difference across its two terminals. Also,express this law mathematically.
$(ii)$ Draw the $V-I$ graph for this law. Justify your answer.
$(iii)$ Write the name and use of the circuit components whose symbols are given below:
$(a)$ $A$ resistor with an arrow through it.
$(b)$ $A$ circle with a dot inside,connected to two lines.

Three incandescent bulbs of $100\, W$ each are connected in series in an electric circuit. In another circuit, another set of three bulbs of the same wattage are connected in parallel to the same source. Will the bulbs in the two circuits glow with the same brightness? Justify your answer.

Why do the wires connecting an electric heater to the mains not glow while its heating element does?