IB Physics HL B 4 5 Hl Entropy Equations Questions

Calculate entropy changes in HL thermodynamics using ΔS=Q/T for reversible transfer, recognising zero change for reversible adiabatic processes and analysing cycles.

Exam points

Calculate entropy change with ΔS=ΔQ/T, using kelvin temperature, energy data and J K⁻¹ units.
Use heat-transfer and reversible/adiabatic conditions to determine the sign of ΔS or justify ΔS=0.
Apply S=kB ln Ω to calculate or compare the number of microstates and explain how microscopic arrangements affect entropy.

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Study B.4.5 (HL)—Entropy equations conceptsOpen the corresponding Concept lesson for explanations, examples and exam connections.

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A student is investigating the emf and internal resistance of a cell, using the circuit shown. The ammeter and the voltmeter are ideal.

Figure for Question IB Physics HL B 4 5 Hl Entropy Equations Questions question 1 — IB Physics HL

The graph shows the variation of the voltmeter reading V with the ammeter reading I.

The student then replaces the variable resistor with an electric heating element in order to investigate the thermal output of the system. The heating element is used to raise the temperature of the water to the boiling point.

After the boiling point is reached, 12 g of the water are vaporized. The specific latent heat of vaporization of water is $2.3 \times 10^{6} \mathrm{Jkg}^{-1}$ .

Calculate the change in entropy of the vaporized water.

Use of $\Delta S=\frac{\Delta Q}{T}$ $=\frac{(0.012 \mathrm{~kg})\left(2.3 \times 10^{6}\right)}{100+273}=74 \mathrm{~J} \mathrm{~K}^{-1}$

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IB Physics HL B 4 5 Hl Entropy Equations Questions question 1