A stretched wire of a material whose young's modulus $$Y=2 \times 10^{11} ~\mathrm{Nm}^{-2}$$ has poisson's ratio 0.25 . Its lateral strain $$\varepsilon_l=10^{-3}$$. The elastic energy density of the wire is
The speed of sound in an ideal gas at a given temperature $$T$$ is $$v$$. The rms speed of gas molecules at that temperature is $$v_{\text {rms }}$$. The ratio of the velocities $$v$$ and $$v_{\text {rms }}$$ for helium and oxygen gases are $$X$$ and $$X^{\prime}$$ respectively. Then, $$\frac{X}{X^{\prime}}$$ is equal to
A positively charged glass rod is brought near uncharged metal sphere, which is mounted on an insulated stand. If the glass rod is removed, the net charge on the metal sphere is
In the situation shown in the diagram, magnitude, if $$q < < |Q|$$ and $$r >>>a$$. The net force on the free charge $$-q$$ and net torque on it about $$O$$ at the instant shown are respectively.
($$p=2 a Q$$ is the dipole moment)