Define superconductivity of a substance.

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 :

When light shines on a $p-n$ junction diode, the current $I$ versus voltage $V$ is observed as in figure below.

In which quadrant(s) does the diode generate power, so that it can be used as a solar cell?

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___

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 $\frac{t_{\mathrm{s}}}{t_{\mathrm{p}}}$?

A $10 \mathrm{V}$ cell of negligible internal resistance is connected in parallel across a battery of emf $200 \mathrm{V}$ and internal resistance $38 \mathrm{\Omega }$ as shown in the figure. Find the value of current in the circuit. 

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

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

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 $R$?

Shown in the figure is a semicircular metallic strip that has thickness $t$ and resistivity $\rho$. Its inner radius is $R_1$ and outer radius is $R_2$. If a voltage $V_0$ is applied between its two ends, a current $I$ flows in it. In addition, it is observed that a transverse voltage $\mathrm{\Delta }V$ develops between its inner and outer surfaces due to purely kinetic effects of moving electrons (ignore any role of the magnetic field due to the current). Then (figure is schematic and not drawn to scale)