☰ Contents · Physics

Laboratory work and Chapter II review

Lessons 26–27 · 2 lessons · P. Habibullayev, A. Boydedayev, A. Bahromov, K. Suyarov, J. Usarov, M. Yuldasheva. Physics Grade 9, revised and expanded 3rd edition. G‘afur G‘ulom Publishing House, Tashkent, 2019
27

Chapter II review: tests and summary

Textbook: pp. 74–80
GoalSummarise the main concepts and formulas of Chapter II; solve test and calculation tasks.
New words
internal energy · ichki energiyaquantity of heat · issiqlik miqdorifirst law of thermodynamics · termodinamikaning birinchi qonuniirreversible process · qaytmas jarayon
Explanation

Chapter formulas: internal energy U = (3/2)νRT = (3/2)pV (monatomic ideal gas), ΔU = (3/2)νRΔT; thermodynamic work A = pΔV = νRΔT (p = const); heat Q = cmΔt, heat balance Q_given = Q_received; fuel Q = qm; first law Q = ΔU + A. Processes: isothermal Q = A; isochoric Q = ΔU; isobaric Q = ΔU + pΔV (A = 0.4Q for a monatomic gas); adiabatic Q = 0, A = –ΔU. Second law: heat does not pass from cold to hot by itself; all heat processes are irreversible. In tests find the process first, watch the signs (A > 0 on expansion, ΔU > 0 on warming) and convert to SI. Lab safety: only adults handle boiling water and hot bodies.

Worked examples
5 mol of helium (monatomic) is heated by 40 K: ΔU = (3/2)νRΔT = 1.5·5·8.31·40 ≈ 2490 J ≈ 2.5 kJ: the internal energy rises by 2.5 kJ.
Test: a gas expands from 3 l to 6 l at 100 kPa. A = pΔV = 10⁵·3·10⁻³ = 300 J (positive because the gas expanded).
Class activity

Chapter “quick test”: the teacher reads 10 questions (e.g. “work in an isochoric process?”); groups answer with A/B/C/D cards. Then analyse mistakes together.

Practice
1
A monatomic gas has p = 200 kPa and V = 0.01 m³. What is the internal energy in J?
2
3 kg of water at 90 °C and 1 kg at 10 °C are mixed. Final temperature (°C)?
3
A gas receives 900 J of heat and does 350 J of work. What is ΔU in J?
4
Why does a thermos keep tea hot for long (in terms of the second law and insulation)?