Melde's Apparatus is a simple way to introduce students  the concept of standing waves. The Electrically Maintained Tuning Fork consists of a heavy nickel plated U-shaped prongs with a vibration rate of 60 per second mounted on sturdy metal base Accurate frequency adjustment can be made with the help of a sensitive electromagnetic coil placed between the prongs. The amplitude of vibrations can also be varied smoothly by sliding the electromagnetic coil back and forth between the prongs. A small spring type strip makes contact with one of the prongs, and a screw point makes contact with the strip. The arrangement can be used in either horizontal or vertical configuration and hence allows two modes of vibration , transverse and longitudinal. The unit operates on 6 Volts, D.C. Supplied with scale pan, bench clamp with pulley but without weights. To show relationships between frequency, length, tension and mass.