Physics Photo of the Week

  September 23, 2022 Moon under a Rainbow - Photo from Sarasota, Florida by Briana Bryant If you look carefully at this image underneath the top of the rainbow you can make out an image of a nearly full Moon.  It's highly unusual to see such an occurrence. First, in order to see a rainbow we need both sunshine and rain.  We must look in the opposite direction of the Sun.  In order to have the rain, most likely the rain would come from a cloud that is in the distance causing the rain.  The raindrops reflect the sunlight by means of the light entering the drops, and internally reflected from the far side of the raindrops, and back to the observers.  As the light enters and leaves each surface the light is bent, and the amount of bend in the light depends on the index of refraction* of the water drop.  Different colors of light exhibit a different index of refraction in water.  That means that the different colors emerge at slightly different angles to the initial direction and the

September 9, 2022 Soupy Physics When tomato soup is heated in a saucepan, we can often see the tops of convection cells.  The darker areas of the soup surface consist of the warmer soup that has risen from the bottom near the heat source.  The fluid spreads from the center of a rising column or, cell, and as the surface cools it falls back toward the bottom of the pan.  Where it falls, it tends to leave the small air bubbles that continue to float on top.  When you watch the soup - before it starts to boil - you can see the soup rising in the center of the cells and propagate towards the cell walls.       The picture at right shows a schematic diagram of the flow of the soup in the pan that is heated by a hot plate from below.  The convection cells are referred to as B énard cells named after the French physicist Henri B énard who studied them extensively in 1900.  The analytical fluid mechanics of the process is very complicated.  The convection flow in an unevenly heated (or cooling