When an ideal gas $\left(\gamma=\frac{5}{3}\right)$ is heated under constant pressure, then what percentage of given heat energy will be utilised in doing external work?

In the given electrical network, the value of resistance ' $R$ ' when the current in the galvanometer will be zero, is

When a photosensitive metal surface is illuminated with radiation of wavelength ' $\lambda_1$ ', the stopping potential is ' $\mathrm{V}_1$ '. If the same surface is illuminated with radiation of wavelength ' $3 \lambda_1$ ', the stopping potential is $\frac{\mathrm{V}_1}{6}$. The threshold wavelength for the photosensitive metal surface is

The mean kinetic energy of the molecules of an ideal gas at $399^{\circ} \mathrm{C}$ is ' E '. The temperature at which the mean kinetic energy of its molecules will be ' $\mathrm{E} / 2$ ', is