A strain gauge (a.k.a strain gage)
is a device whose electrical resistance varies in proportion to the amount of strain applied to the material. The principle behind strain gauges are very simple – each metal has a certain resistance factor. An external tensile force /(compressible force) increases/decreases the resistance by elongating/contracting it. In doing so, When an electrical conductor is stretched within the limits of its elasticity such that it does not break or permanently deform, the amount of induced stress may be inferred by the use of such strain gauges. There are several types of strain gauges, including foil strain gauge, wire strain gauge, and semiconductor strain gauge.