Physics 9702 · AS & A Level · The first law of thermodynamics

The first law of thermodynamics — practice question

(a)[2]

Define specific heat capacity in your own words.

(b)

An ideal gas with mass $0.35\,\text{kg}$ is warmed at a constant pressure of $2.0 \times 10^5\,\text{Pa}$, causing its internal energy to rise by $7600\,\text{J}$. In this change, the volume increases from $0.038\,\text{m}^3$ to $0.063\,\text{m}^3$ and the temperature rises by $56\,^\circ\text{C}$.

(b(i))[1]

Show that the magnitude of the work done on the gas is $5000\,\text{J}$.

(b(ii))[2]

Explain whether the work done on the gas is positive or negative.

(b(iii))[2]

Determine the amount of thermal energy $q$ transferred to the gas.

(b(iv))[2]

Calculate the specific heat capacity of the gas for this process. Give a unit with your answer.

(c)[3]

The gas in (b) is now heated at constant volume instead of at constant pressure. The increase in internal energy of the gas is the same as in (b). Use the first law of thermodynamics to explain whether the specific heat capacity of the gas for this process is less than, the same as, or greater than the answer in (b)(iv).

Worked solution & mark scheme

This 12-mark question has a full step-by-step worked solution and mark scheme. One marking point: Thermal energy needed per unit mass to change temperature

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