Two coherent narrow slits emitting light of wavelength $\lambda$ in the same phase are placed parallel to each other at a small separation of $3\lambda$. The light is collected on a screen $S$ which is placed at a distance $D$ from the slits. Find the smallest distance $x$ from the central point $O$ such that point $P$ is a maxima.

Which one of the following is the correct order of the second ionisation potential of $Na, Ne, Mg$ and $Al$?

$A$ ball of mass $M$ falls from a height $h$ on a floor for which the coefficient of restitution is $e$. The height attained by the ball after two rebounds is

Which of the following molecules has a zero dipole moment?

In an industrial process,$10\, kg$ of water per hour is to be heated from $20^\circ C$ to $80^\circ C$. To do this,steam at $200^\circ C$ is passed from a boiler into a copper coil immersed in water. The steam condenses in the coil and is returned to the boiler as water at $90^\circ C$. How many $kg$ of steam is required per hour? (Specific heat of steam $= 0.5\, cal/g^\circ C$,Latent heat of vaporisation $= 540\, cal/g$,Specific heat of water $= 1\, cal/g^\circ C$)

The coordinates of the focus of the parabola described parametrically by $x = 5t^2 + 2, y = 10t + 4$ are