A Carnot engine having efficiency $60 \%$ receives heat from a source at a temperature 600 K . For the same sink temperature, to increase its efficiency to $80 \%$, then the temperature of the source is

A gaseous mixture consists of 2 moles of oxygen and 4 moles of argon at an absolute temperature $T$. Neglecting all vibrational modes, the total internal energy of the mixture of the gases is

The average translational kinetic energy of the oxygen molecules at a temperature of $127^{\circ} \mathrm{C}$ is

(Boltzmann constant $=1.38 \times 10^{-23} \mathrm{JK}^{-1}$ )

An electric kettle takes 4 A current at 220 V . If the entire electric energy is converted into heat energy, then the time (in minutes) taken to increase the temperature of 1 kg of water from $34^{\circ} \mathrm{C}$ to $100^{\circ} \mathrm{C}$ is