SONOMETER’S ELECTROMAGNET A step down transformer is used for the determination of frequency of A.C. mains, because the voltage of the A.C. mains is 220V, which is dangerous. The step down transformer reduces this voltage to 6/8 volts. Output Voltage : AC 6V & 8V Output Current : 2 Amp. Supplied with connecting leads. Exp No. 91- To determine the frequency of AC mains can be found by using another method--using Horse Shoe Magnet instead of an electromagnet.