Density of water at 4°$4^{\circ}$ C and 20°$20^{\circ}$ C are 1000 kg/m³$1000 \, kg/m^{3}$ and 998 kg/m³$998 \, kg/m^{3}$ respectively. The increase in internal energy of 4 kg water when it is heated from 4°$4^{\circ}$ C to 20°$20^{\circ}$ C is ____J.
(Specific heat capacity of water = 4.2 J/g°C$4.2 \, J/g^{\circ}C$ and 1 atmospheric pressure = 10⁵$10^{5}$ Pa)
Δ U = Q - W$$\Delta U = Q - W$$Δ U = 268800 - 0.8 = 268799.2 J$$\Delta U = 268800 - 0.8 = 268799.2 \text{ J}$$
Pattern Recognition
When heating solids or liquids, the expansion is so small that Δ V$\Delta V$ is negligible, meaning W ≈ 0$W \approx 0$, making Δ U ≈ Δ Q$\Delta U \approx \Delta Q$. Subtracting the exact 0.8J$0.8\text{J}$ provides the highly precise answer required here.
Chapter Mix
Class 11 Physics: Thermodynamics
Class 11 Physics: Thermal Properties of Matter
Practice past-year questions one chapter at a time. Pick an exam → subject → chapter and get every PYQ for that topic — pulled together from all past papers — with the chapter's key formulas alongside.
