Fig. VII.14: A schematic of Switch

A switch ( Fig. VII.14) is a device which has two states of operation viz ., ON and OFF. The duration of the switch to remain in either state can be modulated as per requirement. If and are the switch on and switch off time respectively, then duty cycle of the switch is defined as where is kept constant for any operation. This methods is often called as Pulse Width Modulation (PWM). Transistor and Thyristor are the examples of switches.

A solenoid is a coil wound into a tightly packed helix which produces a controlled magnetic field when an electric current is passed through it. Solenoids can be used as electromagnets which convert electromagnetic energy into linear motion of some mechanical part. It is often used as a valve which actuates a piston to restrict a flow in a pneumatic/hydraulic pipeline.