Q4. Bodies A and B are in thermal equilibrium, and so are B and C. Are A and C in thermal equilibrium? What would happen if they were brought into contact?
Yes. A and C are each in thermal equilibrium with B, so by the zeroth law they are in thermal equilibrium with each other. Their temperatures are equal, and no net heat would flow between them.
Q5. The thermometer of Example 4 (heat capacity 10 J K, at 20 °C) is put into 500 g of water at 60 °C instead. What does it read?
Water: 0.500 × 4186 = 2093 J K. T = (2093 × 60 + 10 × 20)/2103, about 59.8 °C. With ten times as much water, the thermometer disturbs the temperature only about a tenth as much (0.19 °C instead of 1.82 °C).
Q6. Why is it important that a thermometer has a small heat capacity?
It must reach equilibrium with the body by taking or giving only a little heat, so that the body’s temperature hardly changes while it is being measured. A small heat capacity also lets it reach equilibrium quickly.