Op-Amp and MOSFET current source not behaving as expected
This won't work with the TL082 due to (a) not having enough power supply voltage and (b) the inputs don't like to work down towards the negative power rail (0 volts on your diagram).

10 volts is the recommended minimum supply voltage and the input common mode range doesn't cover the range 0 volts to 2 volts. Try picking a rail-to-rail op-amp or one that can handle such a low supply voltage along with the ability for its inputs to work down to 0 volts (LM324 might be worth considering).