To be useful, sensors must control loads that do some useful work! The opamp allows the lowcurrent (microamps) measurement circuit to control a load that needs much more current (milliamps) to operate. Figure 6 Buffer circuit with high-current load Add a blue LED and protection resistor as a load as shown in Figure 6 Heat and cool the thermistor in the three standard conditions and observe the output of the LED. It should get brighter when the thermistor is hot and darker when the thermistor is cold. If not, debug: Test that the LED works with the power supply instead of the op-amp. If you are not getting variation in brightness with temperature but are getting voltage variation, try making R2 a little bigger, like 12 or 15 kiloohms, to match the thermistor's room temperature resistance. Some lab rooms are a little bit too cold, so the divider voltage is a little too small to light a blue LED. This similar divider circuit in Figure 7 without a buffer will not work1 . Why not