What is a relay?

A relay is an electromagnetic switch. An actuating current passed in a coil operates one or more galvanically separated contacts. In fact it is a remote controlled switch capable of switching multiple circuits, either individually, simultaneously or in sequence.    

The most widely used type of relay is electromechanical relay. In electromechanical relays the switching element is a mecahncial contact, actuated by an electromagnet. This is the msot widely used type of relay design. The principal internal functions of the electromechanical relay are:

  1. Conversion of electrical current into  magnetic field
  2. Conversion of magnetic field into a mechanical force
  3. This Mechanical force operates the contacts
  4. Contacts switch and conduct electrical current
Applications of Relay

Typical applications of relays are as follows:
  • Laboratory instruments
  • Telecommunication systems
  • Domestic appliances
  • Traffic control
  • Control of motors & solenoids
  • Air conditioning & heating

Natural Radioactivity in Soil (Bq.Kg-1)


Country
Type of Radioactive Isotope

K-40
U-238
Ra-226
Th-232
India
400
29
29
64
China
440
33
32
41
Japan
310
29
33
28
USA
370
35
40
35
Russia
520
19
27
30
Spain
470
NA
32
33

Mean values are given from wide range of values
Courtesy: UNSCEAR, 2000