In inductive coupling ("electromagnetic induction" or "inductive power transfer", IPT), power is transferred between coils of wire by a magnetic field. The transmitter and receiver coils together form a "transformer" "(see diagram)". An alternating current (AC) through the transmitter coil "(L1)" creates an oscillating magnetic field "(B)" by Ampere's law. The magnetic field passes through the receiving coil "(L2)", where it induces an alternating EMF (voltage) by Faraday's law of induction, which creates an alternating current in the receiver. The induced alternating current may either drive the load directly, or be rectified to direct current (DC) by a rectifier in the receiver, which drives the load. A few systems, such as electric toothbrush charging stands, work at 50/60 Hz so AC mains current is applied directly to the transmitter coil, but in most systems an electronic oscillator generates a higher frequency AC current which drives the coil, because transmission efficiency improves with frequency.