In a strain gauge, the increase in resistance 
depends on the increase in length 
. The variation of with is shown in the graph below.
The strain gauge is connected into a circuit incorporating an ideal operational amplifier (op-amp), as shown in the figure below.
The strain gauge is initially unstrained with resistance 
. Use data from the graph above to calculate the increase in length of the strain gauge that gives rise to a potential of 
at point A in the figure above.
The strain gauge undergoes a further increase in length beyond the value in (a). State and explain which one of the light-emitting diodes, X or Y, will be emitting light.
.
. This implies that the output is negative, and hence, the light-emitting diode X will be emitting light.
