If an electron is moving in the n^th orbit of the hydrogen atom, then its velocity (v_n) for the n^th orbit is given as :

Two identical metal wires of thermal conductivities K₁ and K₂ respectively are connected in series. The effective thermal conductivity of the combination is :

A triangular plate is shown. A force $$\overrightarrow F $$ = 4$$\widehat i$$ $$-$$ 3$$\widehat j$$ is applied at point P. The torque at point P with respect to point 'O' and 'Q' are :

When two soap bubbles of radii a and b (b > a) coalesce, the radius of curvature of common surface is :