I'm sorry you feel that way kiwan. How can I help you?I am stuck
A very very good point.No matter how they are configured an R and a C all by themselves won't make a very good notch filter. If there is an opamp involved it will be a bit better but still not up to your probable expectations. Tell us what you're trying to do and maybe there is a better way.
Mains interference I guess.So why are you asking about a 50 Hz. notch filter, if you need a low pass?
Well I can guess too, but I'm more interested in getting the OP to be specific about his requirements. Just like you in pointing him in the direction of shielding and grounding which will arguably have a greater payoff than a 50 Hz. notch filter made with an R and a C.Mains interference I guess.
Common problem with low level instrumentation equipment.
@kiwan
Do you fully understand earthing and shielding for this application?
Attention to this is more likely to reduce noise.