PHYS110-How Things Work

Notes on Thermodynamics Lab

Questions
The temperature of a desert lake is much cooler than the temperature of desert sand during a sunny afternoon. Can you explain this in terms of the principles being studied in this lab?
The water reflects better than the sand, so the sand become hotter.

How would you expect the temperatures of the lake and sand to compare just before daybreak?
Since the sand absorbs better than the water, it will also emit radiation better than the water. Thus the sand will be cooler than the water at daybreak.

How would the differences between the lake and sand compare if the sand were darker?
Since it would absorb even better, the sand would be even hotter in the daytime. Since it emits better it would be even colder at daybreak.

Would a dark roof on a house make the house more or less heat efficient in the winter?
In daytime it would absorb sunlight better than a light roof, helping to keep the house warmer. At night it would emit radiation better than a light roof making it colder than a house with a light colored roof.