My teacher always asks me to do the experiments on static electricity in winter. I don't know why? What will happen if I conduct the experiment in monsoon?
One of the problems with doing experiments on static electricity is that the static charge can leak away while you're trying to do your measurements, and one of the main ways the charge leaks away is due to humidity of the air. I don't know what the humidity is in Kolkata, but I would guess that it's much higher during the monsoon that it is during the winter. That there will be less charge leakage in the winter and therefore the experiments are easier to do.
If you're interested in pursuing this further, there's a very thorough paper on measurements of air conductivity here (this is a 1.5MB PDF). There are two ways humid air causes leagage of charge. Firstly the water vapour can be ionised and charge flows simply by migration of these ions through the air. Secondly high humidity creates a very thin film of water on surfaces, and charge can flow through this film of water. The paper finds that the two mechanics for charge leakage are roughly comparable.