Practice physics class test — Year 3: ideal gases and thermodynamics.
15 questions drawn at random from a bank of 25, on the block of the programme your teacher is finishing: every attempt is a different test. No penalty for wrong answers, so answer even if you are not sure. At the end you receive by email the correct answer to every question and your weak topics — with an account you see them straight away here on the page. The step-by-step solution unlocks with your first lesson.
A class test is the written test an Italian high-school class sits after each block of the programme; this practice version is multiple choice.
Test in ItalianThe questions of this simulator are in Italian, as in the real exam.
Programme covered by the test
- Boyle’s and Gay-Lussac’s laws, absolute temperature
- Equation of state of ideal gases
- Kinetic theory: temperature and mean kinetic energy
- Internal energy of a monatomic ideal gas
- The first law and the sign convention for heat and work
- Isothermal, isobaric, isochoric and adiabatic processes
- Heat engines and efficiency
- The second law, its statements and the Carnot cycle
Two worked examples from the test
Uno studente scrive: «Se scaldo un gas a pressione costante da 20 °C a 40 °C il volume raddoppia, perché la temperatura è raddoppiata».
Dov'è l'errore?
Solution
Nell'isobara vale con le temperature in kelvin.
Convertendo: e quindi
Il volume aumenta del circa. Il rapporto non significa nulla, perché lo zero della scala Celsius è arbitrario mentre quello della scala Kelvin no: sotto lo zero assoluto non si può scendere.
Regola pratica: in ogni legge dei gas la prima cosa da fare è convertire tutte le temperature in kelvin.
Una bombola rigida contiene un gas a 20 °C alla pressione di 2,0 bar. La si scalda fino a 100 °C.
Quanto vale la pressione finale?
Solution
La bombola è rigida, quindi la trasformazione è isocora: pressione e temperatura assoluta sono direttamente proporzionali.
Sul libro di testo italiano questa è la seconda legge di Gay-Lussac (la prima è l'isobara ); in molti testi in inglese le stesse due leggi si chiamano invece legge di Gay-Lussac (isocora) e legge di Charles (isobara). Il nome cambia, la formula no: quello che conta è quale grandezza tieni costante.
In kelvin: , .
Il valore è quello che si ottiene usando i gradi Celsius (): un errore da cinque volte tanto, il più costoso di tutto il capitolo.
In the online practice test you will find 13 more questions like these; the correct answer to every question arrives by email.
Prefer paper? Download the test as a PDF (15 questions, 4 pages · 84 KB, ready to print). You receive the solutions by email after taking it online.
Download the PDFWhat a physics test on ideal gases and thermodynamics looks like
Processes on the pV diagram to recognise and calculate, the equation of state applied twice, the first law with the balance of heat and work, the efficiency of a heat engine and a comparison with the Carnot cycle.
The mistake that costs the grade
Working in degrees Celsius: the gas laws and the efficiency need kelvin, and a temperature in Celsius gives a meaningless result, often an efficiency greater than one. Right after come the signs of Q and W in the first law, swapped halfway through the exercise.
How to use this practice test
Take it once cold, without revising and with the timer on: it is there to show you where you stand, not to look good. Then look at your weak topics, revise only those — usually two or three, not the whole chapter — and retake it after a few days. The 15 questions are drawn from a bank of 25, so the second attempt is not the same test and the scores are genuinely comparable.
Is the score not enough?
See which topics lost you the most marks, then read the typical physics mistakes in high school — or we look at your results together: the diagnostic is free.