Answer the following questions related to the heating effect of electric current:
(i) State the physical quantities on which the heat produced in a resistor depends when an electric current passes through it for a certain time.
(ii) Explain qualitatively why a thin fuse wire melts when a large current flows through it, whereas a thicker connecting wire carrying the same current does not.
(iii) A heater coil and its connecting leads are made of the same material and carry the same current. Explain why the heater coil becomes red-hot while the leads remain almost at room temperature.