A group of students use the apparatus shown above to determine the thermal conductivity of a certain type of plastic. A hot plate is used to keep water in a container boiling at a temperature of 100°C. They place a slab of the plastic with area 0.025 m² and thickness 0.010 m above the container so that the bottom surface of the slab is at a temperature of 100°C. They put a large block of ice with temperature 0°C on top of the plastic slab. Some of the ice melts, and the students measure the amount of water collected during a time At. The students correctly calculate the amount of energy Q delivered to the ice and thus determine Q/At. They repeat this experiment several times, each time adding an identical slab to increase the total thickness L of plastic. Their results are shown in the table below.

Fig: 1

Fig: 2