To determine the frequency of AC mains, e.m.f of cells and capacity of condenser. A thin steel rod is clamped at one end and passes through a small solenoid. one end of the rod is flattened and a thread is tied to it. the solenoid is connected to AC mains through a suitable lamp resistance. The solenoid and horse shoe magnet cause the rod to vibrate with the frequency of AC supply. Fitted on a wooden board and complete with pulley pan thread.
