K kaleidophone A thin metal bar of rectangular cross section carrying a bead at the upper end and clamped in a vice used to generate vibrations of prescribed frequencies in the different planes of vibration, thus forming characteristic patterns. The frequency of vibrations is the same for the two planes when the cross section of the bar is square or circular. The stiffness of the bar is greater in the plane of greater thickness in case of a rectangular cross section, leading to higher vibration frequency in this plane when compared to the side of smaller thickness. The ratio of vibration frequencies in the two planes can be adjusted to the desired value by appropriate selection of the dimensions of the cross section. The kaleidophone was invented by Wheatstone. A modification of the original design, with the bar divided into two parts, allows the continuous variation of the frequency ratio by changing the location where the bar is clamped.

Kaleidoscope An optical toy consisting of a tube and between two to four plane mirrors. Most kaleidoscopes consist of two or three mirrors, and the mirrors are placed at an angle of 45◦ or 60◦. It produces symmetrical patterns by multiple reflection by the mirrors. Frontsurface-mirrors are used to generate a clear image. Objects are illuminated at one end of the tube and the image is observed through a small hole at the other end.