The density of a mixture of $He$ and $O_2$ gases at $27 \, ^oC$ and $760 \, torr$ is found to be $0.543 \, g \, dm^{-3}$. What is the mass percentage of helium in the mixture?

If an electric heater is rated at $1000\, W$,then the time required to heat one litre of water from $20\, ^oC$ to $60\, ^oC$ is

$A$ plane passes through $(2,3,-1)$ and is perpendicular to the line having direction ratios $3,-4,7$. The perpendicular distance from the origin to this plane is

In the circuit shown,a meter bridge is in its balanced state. The meter bridge wire has a resistance of $0.1 \ \Omega/cm$. Find the value of the unknown resistance $X$ and the current drawn from the battery of negligible internal resistance.

The first terrestrial plants are .......

$A$ fully charged capacitor $C$ with initial charge $q_0$ is connected to a coil of self-inductance $L$ at $t=0$. The time at which the energy is stored equally between the electric and the magnetic field is