The correct answer is: A. current
An induction cup relay is a type of relay that uses the principle of electromagnetic induction to operate. When a current flows through the coil of the relay, it creates a magnetic field. This magnetic field attracts a metal cup, which closes the contacts of the relay. The contacts of the relay can be used to control a circuit, such as turning on a light or starting a motor.
The induction cup relay is operated due to changes in current. When the current in the coil changes, the magnetic field also changes. This change in magnetic field causes the metal cup to move, which closes or opens the contacts of the relay.
The induction cup relay is a very sensitive device and can be used to detect very small changes in current. It is often used in industrial applications where it is necessary to control a circuit based on very small changes in current.
The other options, voltage and impedance, are not correct. The induction cup relay is not operated due to changes in voltage or impedance.