(a) A potential difference $V$ is applied across the ends of a cylindrical conductor of length $l$, area of cross-section $A$ and resistance $R$. It is gradually stretched till its length is tripled. How will (i) the drift speed of electrons in the conductor, and (ii) the resistance of the conductor be affected ? Justify your answers. (b) In the given circuit diagram, find the potential difference between points $B$ and $D$. OR (a) A cell of emf $E$ and internal resistance $r$ is connected across a resistor of variable resistance $R$. Draw a plot showing the variation of (i) the current ($I$) in the circuit with $R$, and (ii) the terminal potential difference of the cell with $R$. (b) The resistance of a heating coil is $100\;\Omega$ at $25^\circ\text{C}$ and $120\;\Omega$ at $1025^\circ\text{C}$. (i) Find its resistance at $425^\circ\text{C}$. (ii) Draw a plot showing variation of its resistance as a function of increase in temperature.