Which of the following materials obeys the nature of given voltage-current $(V-I)$ graph under constant temperature?

The equivalent resistance between the points A and B is

In the given circuit, total power consumed is $200 \mathrm{W}$. The value of resistance $R$ is

The emf of a cell is $1.6 \mathrm{V}$. On connecting external $15\Omega$ resistance across the cell, the terminal potential difference falls to $1.5 \mathrm{V}$. The internal resistance of the cell is

The resistance of the four arms $P, Q, R$ and $S$ in a Wheatstone's bridge are $2\Omega ,4\Omega ,4\Omega$ and $8\Omega$ respectively as shown in figure. Current through the galvanometer will be

The length $AB$ of slide wire bridge is $100 \mathrm{cm}$ long. Where should be free end of the galvanometer be connected on $AB$ so that galvanometer may show zero deflection?