At what angle should an unpolarised beam be incident on a crystal of refractive index $\mu = \sqrt{3}$,so that the reflected beam is completely polarised (in $^o$)?

$A$ cell of $emf$ $E$ has an internal resistance $r$ and is connected to a rheostat. When the resistance $R$ of the rheostat is changed,which is the correct graph of the potential difference $V$ across it?

The system shown in the figure is in equilibrium and at rest. The spring and string are massless. Now,the string is cut. The acceleration of mass $2m$ and $m$ just after the string is cut will be:

If the pair of straight lines given by $Ax^2 + 2Hxy + By^2 = 0$ $(H^2 > AB)$ forms an equilateral triangle with the line $ax + by + c = 0$,then $(A + 3B)(3A + B)$ is equal to:

The solution of $(1+x^2) \frac{dy}{dx} + 2xy - 4x^2 = 0$ is:

Tetrarch vascular bundles are found in .......