When no current flows through a conductor,

A battery has an $\mathrm{e}\mathrm{m}\mathrm{f}$ of $15\mathrm{ }\mathrm{V}$ and internal resistance of $1 \mathrm{\Omega }$ . The terminal to terminal potential difference is less than, equal to or greater than $15\mathrm{ }\mathrm{V}$, if the current in the battery is

(1) from negative to positive terminal,

(2) from positive to negative terminal,

(3) zero current?

The internal resistances of two cells shown are $0.1 \mathrm{\Omega }$ and $0.3 \mathrm{\Omega }$. If $R=0.2 \mathrm{\Omega }$, the potential difference across the cell

Find the current flowing through the resistance $R_1$ of the circuit shown in figure if the resistances are equal to $R_1=10 \mathrm{\Omega }, R_2=20 \mathrm{\Omega }$ and $R_3=30 \mathrm{\Omega }$ and the potentials of points $1, 2$ and $3$ are equal to ${\mathrm{\phi }}_1=10 \mathrm{V}, {\mathrm{\phi }}_2=6 \mathrm{V}$ and ${\mathrm{\phi }}_3=5 \mathrm{V}$.

If a wire is stretched to make it $0.2\%$ longer, its resistance will be