1.1. The apparatus shown in Fig. 1.1 is known as Leslie’s Differential Air Thermometer.

Fig. 1.1

The heater is switched off. Tap T is opened so that the air on the two sides of T has the same pressure. Tap T is then closed.

(i) The heater is switched on. On Fig. 1.1, mark clearly where the two liquid levels might be a short time later. 

[1]

(ii) Explain your answer to (a)(i).

[2]

1.2. A gym has a low initial temperature. A larger radiant heater is placed on the floor in the centre of a gym to heat the room. The room has no open windows or ventilation. 

Describe and explain the subsequent motion of air in the gym, naming any processes. 

1.3. After a marathon in winter, the athlete has sweated a large amount. 

(i) Explain why this could be dangerous.

[3]

(ii) Some athletes choose to wear a shiny foil blanket immediately after a race. Explain why.

[3]

1.4. For the end of the marathon, the athlete's coach has a double-walled vacuum flask (Fig. 1.2), which is designed to maintain the temperature of its contents. It is partially filled with a hot liquid.

The lid is made of black plastic and sealed tight. The walls are silvered metal.

Eventually the liquid cools. Explain how thermal energy is transferred from the hot liquid through the lid over time.