5CH - 2007 Q27 Op amps

Solution to another Higher paper question with the differential op amp as a monitoring circuit. Some of you struggled with (b) (ii) - we haven't covered MOSFETs in class yet but you should still be able to figure out how changing the value of one resistor affects the potential at the points in a wheatstone bridge.

In this example, changing Rth causes an increase in the voltage across Rth. This means that resistor Z has less of a voltage across it and therefore there is less of a voltage a point Q.