Why reactive elements are noise free and only resistors are responsible for noise ?

Hi...It might be a very basic question..but I'm nt exactly clear on why is it that reactive elements (Inductors, Capacitors) are noise free and why is it that resistors alone are responsible for the noise in a circuit?

Hi.

In an ideal world, there is no such thing as noise (eg. simulators).

But in the real world, there is electro magnetic signals everywhere, even on an abandon earth without people, there will be electromagnetic noise.

A resistor will pick up some of that noise, even if the noise level is so small that you cannot measure it, it's still there.
And in high sensitive equipment, that noise should be taken in acount when constructing that equipment.

Also, inductor does consist of small parasitic capasitances. That will cause any inductor to have its own resonant frequenzy.

A resistor will also consist of parasitic inductors and capacitors that could give it some unpredictable properties at high frequensis.

caps and inductors has their ESR and NF contribution by these low parasitic resistance will not contribute much.
For ultra LNA design, one should consider these too.

I think that the question refers to thermal noise, which is properly calculated by simulators.

Ideal inductors and capacitors (purely reactive) have no resistance and do not contribute to thermal noise. For "real" components, the parasitic resistors will contribute to noise.

Best regards
Volker

how can u simulate real r,l,c in a simulation software such as Hspice?

Most component vendors provide equivalent circuit models which include the parasitics. For example, a simple model for an SMD inductor might have series L-R and parallel C (self resonance).