Different material of two identical long bars $A$ and $B$ are coated with wax and have their one end immersed in a hot oil bath. When the steady state is reached, the lengths for which wax melt are $l_A$ and $l_B$. If $k_A$ and $k_B$ are thermal conductivities of materials, then

A gas is at constant pressure $4 \times 10^5 \mathrm{~N} / \mathrm{m}^2$. When a heat energy of 2000 J is supplied to the gas, its volume changes by $3 \times 10^{-3} \mathrm{~m}^3$. What is the increase in its internal energy?

Certain amount of heat supplied to an ideal gas under isothermal condition will result in

A heating element of mass 100 g and having specific heat of $1 \mathrm{~J} /\left(\mathrm{g}^{\circ} \mathrm{C}\right)$ is exposed to surrounding air at $27^{\circ} \mathrm{C}$. The element attains a steady state temperature of $127^{\circ} \mathrm{C}$, while absorbing 100W of electric power. If the power is switched Off, then approximate time taken by the element to cool down to $126^{\circ} \mathrm{C}$ will be (neglect radiation)