The Ideal Gas and the First Law of Thermodynamics

How the real exam tests it

Questions from real CSCA papers that test this concept. Work each one out before you open the answer.

1. CSCA Physics December 2025 Past Paper
   An ideal gas of a certain mass undergoes an isobaric process (constant pressure) from state A to state B. Given that the volume of state A is $V _ { 1 } = 1.5 \mathrm {~m} ^ { 3 }$ and its temperature is $T _ { 1 } = 300 \mathrm {~K}$, while the temperature of state B is $T _ { 2 } = 400 \mathrm {~K}$, the volume of state B is ( ).
   • A．$1.5 \mathrm {~m} ^ { 3 }$
   • B．$4.5 m ^ { 3 }$
   • C．$2 m ^ { 3 }$
   • D．$6 m ^ { 3 }$
   Show answer & solution

   Answer: C

   For a fixed mass of ideal gas at constant pressure, $V_1/T_1 = V_2/T_2$. Thus $V_2 = 1.5\times(400/300) = 2\,\mathrm{m^3}$ exactly. Option C is correct.
   See it in the full CSCA Physics December 2025 Past Paper
2. CSCA Physics March 2026 Past Paper
   For an ideal gas at constant pressure, if volume increases, then
   • A．Temperature increases
   • B．Temperature decreases
   • C．Internal energy unchanged
   • D．Releases heat
   Show answer & solution

   Answer: A

   PV = nRT: P constant, V up → T up. Higher T = greater molecular kinetic energy = more internal energy (not C). Isobaric expansion: gas does work and absorbs heat (not D). Answer: A.
   Take the full CSCA Physics March 2026 Past Paper — timed & graded
3. CSCA Physics April 2026 Past Paper
   A fixed mass of gas undergoes an isochoric (constant-volume) process. Its temperature rises from $27 ^ { \circ } \mathrm { C }$ to $54 ^ { \circ } \mathrm { C }$. The pressure becomes ( ) times its original value.
   • A．1.09
   • B．1
   • C．2
   • D．1.5
   Show answer & solution

   Answer: A

   For an isochoric process, $\frac { P } { T } =$ constant ( $T$ in kelvin). $T _ { 1 } = 27 + 273 = 300 \mathrm {~K}$, $T _ { 2 } = 54 + 273 = 327 \mathrm {~K}$. $\frac { P _ { 2 } } { P _ { 1 } } = \frac { T _ { 2 } } { T _ { 1 } } = \frac { 327 } { 300 } = 1.09$.
   Take the full CSCA Physics April 2026 Past Paper — timed & graded