How much is the gain of this Op Amp?
In theory, this is basically a inverting amplifier with gain of 1 (overall gain of -1).  However, in practise there are significant problems with this circuit:

You forgot to hookup power!  Opamps need separate power to work, and in your case it needs both a positive and negative supply.  Note that the TL081 requires significant output headroom at each end.  The power supply voltage matters, and tells us what operating range you are expecting.

R2 does nothing.  The TL081 is a FET input opamp, so 50 &Omega; in series with one of its inputs is just silly.  The positive input of the opamp is tied to ground either way.

R1 and R3 are connected around the opamp in classic inverting amplifier configuration.  The gain is always negative, and its magnitude is R3/R1, which in this case is 1.  However, you also have to consider the current capability of the opamp.  100 &Omega; is very low, and will require significant current.  I haven't looked it up (that's your job), but I expect the TL081 is only good for a few 10s of mA.  It might work over its whole range with 1 k&Omega; resistors, but likely not with 100 &Omega; resistors.  Since you haven't connected power, and we therefore don't know what voltage range you expect this to work over, we can't really say what will happpen.

100 &Omega; is a very heavy output load for a TL081.  Again, look up the current capability of the opamp.

What's the point of the 100 &Omega; output resistor (Argh, no component designator!)?  Even if the other issues above are solved, we can only guarantee the circuit function from the input to the opamp output.  What happens at Output is also a function of the load, which you don't show.

Your statement of 500 mA input current makes no sense at all.  Actually think about it.  (500 mA)(100 &Omega;) = 50 V.  That's how much would be across each of R1 and R3.  While you could get a 100 &Omega; resistor that can take 50 V and dissipate 25 W, 50 V is way out of spec for being between any two terminals of a TL081.



TI publishes a datasheet for this part for a reason.  Read it.