What is meant by "electrical resistance" of a conductor? State how the resistance of a conductor is affected when $(i)$ a low current passes through it for a short duration; $(ii)$ a heavy current passes through it for about $30$ seconds.

(N/A) Electrical resistance is the property of a conductor to oppose the flow of electric current through it.
$(i)$ When a low current passes through a conductor for a short duration, the temperature of the conductor does not change significantly. Therefore, the resistance remains constant.
$(ii)$ When a heavy current passes through a conductor for about $30$ seconds, the conductor heats up due to the heating effect of electric current $(H = I^2Rt)$. Since the resistance of a metallic conductor increases with an increase in temperature, the resistance of the conductor will increase.