Humidity, eclipses and early scientists

Solution and notes

These notes look first at the random exchanges of molecules, and of energy, that occur between liquids and gases, and at how humidity is defined and measured. Next is a description of attempts to reconcile observations of eclipses with models of the Earth. Finally, we introduce some scientists who contributed to our knowledge of numbers, light and electromagnetism

Are you sitting comfortably? Your answer will partly depend on the light levels, the temperature, the ventilation and the humidity of your environment, all of which need to be controlled for our comfort. You will be aware that humans sweat as part of the body’s way of regulating temperature, but let us review what is really going on.

Within liquids (and gases…and, indeed, solids) the molecules exchange energy randomly. If there are frequent collisions between molecules in a sample, the distribution of kinetic energy settles to a steady pattern and the sample is said to be in thermal equilibrium. The distribution of kinetic energy is known as the Maxwell-Boltzmann distribution (Figure 1). The peak of the graph shifts to the right as temperature rises.