The work function of a photosensitive metallic surface is $h v_0$. If photons of energy (2.5) $h v_0$ fall on this surface, the electrons come out with maximum velocity ' v '. When the photon energy is increased to $7 \mathrm{~h} v_0$, the maximum velocity of photoelectrons will be
A magnet having a magnetic dipole moment ' M is placed in two magnetic fields ' $\mathrm{B}_1$ ' and ' $\mathrm{B}_2$ ' respectively. If it is displaced slightly from the equilibrium position, it oscillates 60 times in 20 second in field ' $\mathrm{B}_1$ ' and 60 times in 30 second in field ' $B_2$ '. The ratio of field ' $B_1$ ' to that of ' $\mathrm{B}_2{ }^{\prime}$ is
Two objects A and B are separated horizontally by distance ' a '. Object B moves in a direction perpendicular to distance ' $a$ ' with velocity ' $V_1$ '. Simultaneously object A covers shortest distance with velocity ' $V$ ' and meets object $B$ in time ' $t$ '. The time ' $t$ ' is given by
Pressure of the gas remaining same, the temperature at which r. m. s. speed of the gas molecules is double its value at $27^{\circ} \mathrm{C}$ is