A cell of internal resistance $\mathrm{r}$ drives current through an external resistance $\mathrm{R}.$ The power delivered by the cell to the external resistance will be maximum when:

In the figure shown, what is the current (in ampere) drawn from the battery? You are given:
$R_1=15 \mathrm{\Omega }\mathrm{ }, R_2=10 \mathrm{\Omega }\mathrm{ }, R_3=20 \mathrm{\Omega }\mathrm{ }, R_4=5 \mathrm{\Omega },\mathrm{ }{R}_5=25 \mathrm{\Omega },\mathrm{ }{R}_6=30 \mathrm{\Omega },\mathrm{ }E=15 \mathrm{V}$

In the given circuit, an ideal voltmeter connected across the $10 \mathrm{\Omega }$ resistance reads $2\mathrm{ }\mathrm{V}$ . The internal resistance $r$, of each cell is:

In an experiment, the resistance of a material is plotted as a function of temperature (in some range). As shown in the figure, it is a straight line.

One may conclude that