IB Physics HL B.4.5 Entropy equations Question Bank

Practise IB Physics HL B.4.5 by applying entropy equations concepts to exam-style physics questions.

Exam points

identify the relevant physical quantity, model or diagram
apply the correct equation and units to the evidence
justify the result using conservation laws, forces or energy relationships

[Maximum number: 2]

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 B.4.5 (HL)—Entropy equations 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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B.4.5 (HL)—Entropy equations question 1