Non inverting Op amp resistors
does it matter if the resistor is 200ohms or even 200k? Will it affect
  anything ? – Q.T.π


If the feedback resistor is 200 ohms then the grounding resistor needs to be 1 ohm and, the impact of this is that the op-amp's output has to drive a load of 201 ohms. So, if the op-amp is connected to the standard +/- 15 volt rails and is capable (or expected) to deliver an output range from -12 volts to +12 volts, at extremes, the output current will be very nearly 60 mA and far too much for most op-amps.

A typical limit might be 10 mA or even 5 mA.

So based on a 5 mA limit at 12 volts, the feedback resistor and grounding resistor should have a combined resistance of not less than 12/0.005 = 2400 ohms or \$R_F\$ = 2390 ohms and \$R_G\$ = 12 ohms (or nearest equivalent value).

But 5 mA may still be too much (in some applications) and you might go for 10 kohm and 499 ohm.

But why not go to 200 kohm and 1 kohm?

There are usually two answers to this: -


Input bias currents might start to produce a significant DC offset error
The value of 200 kohm for \$R_F\$ combined with the parasitic capacitance around the feedback node might mean that the amplifier runs out of steam at frequencies where performance is still expected.


For point 2 with \$R_F\$ = 200 kohms and a parasitic capacitance of 2 pF, the 3 dB point becomes about 400 kHz and this just may be too low. The only resort you have is to reduce \$R_F\$ and, taking it down to 20 kohm means that you get a bandwidth of 4 MHz for instance.

So, it's a balancing act of these things: -


Choice of op-amp
Battery life
DC error budget
AC high frequency performance