Thermal Equilibrium & Zeroth Law - UNSOLVED PRACTICE SET

Q7. State the Zeroth Law of Thermodynamics in your own words. Why is it called the "Zeroth" law?

Q8. Explain why two bodies at different temperatures, when placed in thermal contact, eventually reach the same temperature.

Q9. Can two bodies be in thermal equilibrium without being in physical contact? Explain with an example.

Q10. What is a thermodynamic system? Give two examples of thermodynamic systems from everyday life.

Q11. Explain the difference between thermal equilibrium and mechanical equilibrium with one example for each.

Q12. Why does a thermometer need to be kept in contact with a patient's body for some time before reading the temperature? Relate this to the concept of thermal equilibrium.

Q13. Explain the concept of thermal equilibrium with a real-life example. Describe how the Zeroth Law of Thermodynamics provides the logical basis for the measurement of temperature. Why is this law considered fundamental despite being stated after the First and Second Laws?

Q14. A student places three metal blocks — copper, aluminum, and iron — in an oven at 150°C for a long time. She then removes them and places them on a wooden table. After some time, she touches each block.

(i) Will all three blocks feel equally hot to her hand? Why or why not?

(ii) If she leaves them on the table for several hours, what will eventually happen to their temperatures?

(iii) Explain which law of thermodynamics governs this final state.

Q15. Describe the process of calibrating a mercury thermometer. Explain how the Zeroth Law ensures that the thermometer readings are meaningful and consistent across different objects and situations.

Q16. In a school experiment, three metal rods A, B, and C are placed in a large insulated container. Initially, the temperatures are: T_A = 30°C, T_B = 50°C, T_C = 50°C. The rods are arranged such that A is in contact with B, and B is in contact with C.

(i) After sufficient time, what will be the temperature of rod B?

(ii) Will rod A and rod C be in thermal equilibrium? Justify using the Zeroth Law.

(iii) If rod B is now removed, and A and C are placed in direct contact, will heat flow? Explain.

Q17. A doctor uses a digital thermometer to check a patient's fever. The thermometer reads 37.5°C after 2 minutes of contact.

(i) Explain why the thermometer reading stabilizes at 37.5°C and does not keep changing.

(ii) If the room temperature is 25°C, why doesn't the thermometer show 25°C instead?

(iii) A second thermometer is placed in contact with the first thermometer. What reading would you expect? Which law explains this?

Q18. Two identical copper blocks, each of mass 500 g, are at temperatures 80°C and 20°C respectively. They are placed in thermal contact inside a perfectly insulated container. The specific heat capacity of copper is 0.385 J g⁻¹ °C⁻¹.

(i) Calculate the final equilibrium temperature of the system.

(ii) Calculate the total heat exchanged between the two blocks.

(iii) Explain why the final temperature is not simply the average of 80°C and 20°C.