It is so wonderful that there are such "theoretical questions" that make us think and reveal the ideas behind mysterious circuits. When I read this question, my knee-jerk reaction was that this is impossible. But the problem remained dormant in my head, and at some point I began to make a connection with the somewhat strange circuit of an *amplifier with a T-bridge in the negative feedback*. Basic idea ========== ... is extremely simple: According to Ohm's law, the current flowing through a resistor R with applied voltage V across it is I = V/R. If we actually supply the resistor with, for example, ten times lower voltage, the current will also decrease ten times (I = V/10R) and it will appear that the resistance has increased ten times (R = 10V/R). Of course, there is a "small" catch here (as in any circus trick:-) - ***we see the voltage V when actually a voltage of V/10 is applied***. Implementation ============== Ohm's circuit with true 10 k resistance ----------------- As an example, the current flowing through a 10 k resistor R with applied 10 V voltage V across it is I = 1 mA. We know that the resistance is 10 k but we can also measure the current and calculate the resistance - R = V/R = 10 V/1 mA = 10 k. <!-- Begin schematic: In order to preserve an editable schematic, please don't edit this section directly. Click the "edit" link below the image in the preview instead. --> ![schematic](https://i.sstatic.net/GhdSX.png) <!-- End schematic --> [![STEP 1][1]][1] Inverting amplifier with true 10 k R2 ----------------- As another example, the 10 k resistor R2 and R1 set a gain of -1 of an op-amp inverting amplifier. <!-- Begin schematic: In order to preserve an editable schematic, please don't edit this section directly. Click the "edit" link below the image in the preview instead. --> ![schematic](https://i.sstatic.net/Oyb7A.png) <!-- End schematic --> [![STEP 2][2]][2] Ohm's circuit with virtual 100 k resistance ----------------- <!-- Begin schematic: In order to preserve an editable schematic, please don't edit this section directly. Click the "edit" link below the image in the preview instead. --> ![schematic](https://i.sstatic.net/mIJmc.png) <!-- End schematic --> [![STEP 3_1][3]][3] [![STEP 3_2][4]][4] Inverting amplifier with virtual 100 k R2 ----------------- <!-- Begin schematic: In order to preserve an editable schematic, please don't edit this section directly. Click the "edit" link below the image in the preview instead. --> ![schematic](https://i.sstatic.net/TCq5z.png) <!-- End schematic --> [![STEP 4_1][5]][5] [![STEP 4_2][6]][6] Inverting amplifier with *T bridge* instead R2 ----------------- <!-- Begin schematic: In order to preserve an editable schematic, please don't edit this section directly. Click the "edit" link below the image in the preview instead. --> ![schematic](https://i.sstatic.net/iZumt.png) <!-- End schematic --> [![STEP 5][7]][7] [1]: https://i.sstatic.net/sBYk3.png [2]: https://i.sstatic.net/S6sFy.png [3]: https://i.sstatic.net/14vTT.png [4]: https://i.sstatic.net/4k4QE.png [5]: https://i.sstatic.net/xfiUA.png [6]: https://i.sstatic.net/Y0kAG.png [7]: https://i.sstatic.net/T07LS.png