Diffusion current in a $p$-$n$ junction is greater than the drift current in magnitude when:

The height of water in a tank is $H$. The range of the liquid emerging out from a hole in the wall of the tank at a depth $\frac{3H}{4}$ from the upper surface of water will be

$A$ gramophone record is revolving with an angular velocity $\omega$. $A$ coin is placed at a distance $R$ from the centre of the record. The static coefficient of friction is $\mu$. The coin will revolve with the record if

Which of the following plants is commonly used as green manure?

If $(2, -1, 3)$ is the foot of the perpendicular drawn from the origin to a plane,then the equation of that plane is

$A$ and $B$ are two substances undergoing radioactive decay in a container. The half-life of $A$ is $15 \ min$ and that of $B$ is $5 \ min$. If the initial concentration of $B$ is $4$ times that of $A$ and they both start decaying at the same time,how much time will it take for the concentration of both of them to be same? $.......... \ min$