A strain gauge S is connected into the circuit shown in the figure below.
The operational amplifier (op-amp) is ideal. The output potential 
of the circuit is given by the expression
State the name given to the ratio 
.
The strain gauge S has resistance 
when not under strain. Calculate the magnitude of 
such that, when the strain gauge S is not strained, the output is zero.
In a particular test, the resistance of S increases to 
. is unchanged. The ratio is 12. Calculate the magnitude of .
.
(or 
).
