# Mosfet gate resistor vs Gain

I have a small question. I was doing a lab with MOSFET 2N7000. The circuit is something like the one below:

There was a question asking if the gain should change if the resistor R1 was changed to 10K? The teacher said the gain should change (slightly) but I did not see any change on the Oscilloscope.

Can someone please advice whether the gain would change if R1 is increased?

• Are you sure the gain change was not predicated on R1 being before R2? In that arrangement, the pair of resistors acts as a voltage divider, so gate voltage would drop on increasing R1, hence leading to lower gain. – Anindo Ghosh May 21 '14 at 4:30
• @AnindoGhosh, R2 connects after R1 which is used for complete switching off of the fet. But why would the gain decrease when increasing R1? – David Norman May 21 '14 at 4:34
• Is this the complete circuit? or you have any biasing part? Is there anything connected to drain other than your Oscilloscope?? – nidhin May 21 '14 at 5:30
• @DavidNorman ideally mosfet gate current is zero and hence whatever be value of $R_1$, you will get Vgs =5V. And hence Vds/Vgs will also remain the same – nidhin May 21 '14 at 6:46
• @David: I suppose you mean "decreased a bit" - and that would be correct. However, I doubt if such a small change can be observed on the scope. – LvW May 21 '14 at 6:58