At this exhibit visitors control a small heater that is immersed in a thin vertical tank of water. This tank sits between a point light source and a white wall. When the heater is turned on, the water heats and rises due to convection currents. This is visible on the white wall because the heated water, which is less dense than cooler water, refracts (bends) the light from the point source more than the cool water around it. A beautiful display of the convection results. The light source can be moved closer to or further away from the tank, changing the magnification of the projected image. Visitors also manipulate the rate of heating, increasing or decreasing the rate convection current.
The Critical Angle exhibit enables visitors to explore properties of refracted light. The round edge of a plastic semicircle is placed in front of a light source. Visitors slowly turn the semicircle clockwise and notice that the light beam bends as it leaves the flat side of the plastic semicircle. When a light beam passes from clear plastic to air at an angle, it bends. As the angle increases, more light reflects and ultimately no light escapes the plastic.
Visitors lower two glass rods into a thin vertical tank filled with oil. One rod "disappears" while the other does not. The disappearing glass rod is made of Pyrex glass which has the same index of refraction as the oil in which it is immersed. Light travels from the oil to the Pyrex glass and out again without bending. As far as light is concerned, there is no difference between the rod and the oil. The other rod is made of flint glass and has a different index of refraction than the oil. When light passes from the oil to the other rod and out again, it bends enabling it to be seen.
Visitors find out why a convex lens is just a fancy hole. This exhibit consists of: a mounted, strongly illuminated, black and white transparency; a white, mobile screen; and an assortment of paddles, with convex lenses of different focal lengths, and various arrangements of holes. By holding the paddles between the screen and transparency, visitors can project an image of the transparency onto the screen. When light passes through a lens, the light bends. Convex lenses, like the ones in this exhibit, bend light rays so that they come together and form an image. When light passes through small holes, images can also be formed.
This exhibit demonstrates the limitations on the ability of the eye to focus on nearby objects imposed by the minimum size of our contracted pupils and the minimum focal length of our lenses. Visitors focus as close as possible on a brightly lit object, then focus as close as possible on the same object through a pinhole. The pinhole image is sharper because it blocks the most divergent light rays, allowing only that light through which is already nearly in focus.
Prisms, typically made of glass, separate white light into the different wavelengths of visible light that combine into white light. The result is a rainbow, visible because different colors of light bend at different angles when they pass through a clear material. The Prism Tree is a simple sculptural exhibit that looks like an 8 foot tall metal tree with a series of prisms hanging from it. Visitors can hold them up to their eyes and look all around at the rainbow effect created everywhere.