The coefficient of cubical expansion of mercury is $$0.00018 /{ }^{\circ} \mathrm{C}$$ and that of brass $$0.00006 /{ }^{\circ} \mathrm{C}$$. If a barometer having a brass scale were to read $$74.5 \mathrm{~cm}$$ at $$30^{\circ} \mathrm{C}$$, find the true barometric height at $$0^{\circ} \mathrm{C}$$. The scale is supposed to be correct at $$15^{\circ} \mathrm{C}$$.
One mole of an ideal diatomic gas undergoes transition from A to B along a path AB as shown below.
The change in internal energy of the gas during the transition is
Assertion : It is hotter over the top of a fire than at the same distance on the sides.
Reason : In the upward direction, the heat propagate through convection.
Assertion : In adiabatic expansion the product of $$p$$ and $$V$$ always decreases.
Reason : In adiabatic expansion process, work is done by the gas at the cost of internal energy of gas.