$A$ mercury drop of radius $1 ~cm$ is sprayed into $10^6$ drops of equal size. The energy expended in joules is (Surface tension of mercury is $460 \times 10^{-3} ~N/m$)

$y + x^2 = \frac{dy}{dx}$ has the solution

Guard cells are helpful in:

The moment of inertia of a meter scale of mass $0.6\, kg$ about an axis perpendicular to the scale and located at the $20\, cm$ position on the scale in $kg\, m^2$ is (Breadth of the scale is negligible).

The wavelength of the first line in the Balmer series in the hydrogen spectrum is $\lambda$. What is the wavelength of the second line?

Photoelectric emission is observed from a metallic surface for frequencies $v_1$ and $v_2$ of the incident light $(v_1 > v_2)$. If the maximum values of kinetic energy of the photoelectrons emitted in the two cases are in the ratio $1: n$,then the threshold frequency of the metallic surface is