In the adjoining figure, the reading of ammeter $A$ is not zero, while that of voltmeter $V$ is zero. The substance $C$ is,

A conducting wire of length $l$, area of cross-section $A$ and electric resistivity $\rho$ is connected between the terminals of a battery. A potential difference $V$ is developed between its ends, causing an electric current. If the length of the wire of the same material is doubled and the area of cross-section is halved, the resultant current would be___

An electric cable having a resistance $R$ delivers $11 \mathrm{kW}$ of power at $220 \mathrm{V}$ to a factory. If the efficiency of transmission is $91\%$, then what is the value of $R$?

Three resistors having resistances $r_1, r_2$ and ${\mathrm{r}}_3$ are connected as shown in the given circuit. The ratio $\frac{i_3}{i_1}$ of currents in terms of resistances used in the circuit is :

A heating coil of resistance $100 \mathrm{\Omega }$ takes $100 \mathrm{s}$ to boil certain amount of water. If a similar heating coil is connected in series with the heating coil, then the time required to boil the water is $t_{\mathrm{s}}$, while $t_{\mathrm{p}}$ time is required to boil the same amount of water if the coils are connected in parallel. What will be $\frac{t_{\mathrm{s}}}{t_{\mathrm{p}}}$?

The unit of current element is $\underline{ }$
 

The current flowing through a wire depends on time as $I=3t^2+2t+5.$ The charge flowing through the cross section of the wire in time from $t=0$ to $t=2 \mathrm{s}$ is

The potential difference between points $A$ and $B$ of adjoining figure is