The ratio of kinetic energy to the total energy of an electron in a Bohr orbit of the hydrogen atom, is

At what temperature will the rms speed of oxygen molecules become just sufficient for escaping from the Earth’s atmosphere?
(Given : Mass of oxygen molecule (m) = 2.76 × 10^–26 kg, Boltzmann’s constant k_B = 1.38 × 10^–23 J K^–1)

A set of n equal resistors, of value R each, are connected in series to a battery of emf E and internal resistance R. The current drawn is I. Now, the n resistors are connected in parallel to the same battery. Then the current drawn from battery becomes 10I. The value of n is

The efficiency of an ideal heat engine working between the freezing point and boiling point of water, is