Two wires of resistance $R_1$ and $R_2$ have a temperature coefficient of resistance ${\alpha }_1$ and ${\alpha }_2$, respectively. These are joined in series. The effective temperature coefficient of resistance is

Assertion :- As temperature of a metallic current carrying the wire is increased, its resistance increases.

Reason :- Decrease in temperature results in a decrease of electric field strength along the conductor so that the current reduces.

$A$ and $B$ are two points on a uniform ring of resistance $19 \mathrm{\Omega }.$ The angle $\angle AOB=45°$. The equivalent resistance between $\mathrm{A}$ and $\mathrm{B}$ is

If the ammeter in the given circuit reads $2 \mathrm{A}$, the resistance $R$ is