 Anyway, coming back to our syllabus, so the first section is about what? Micro factors affecting the movement of charge or micro. So, we will be studying that right now, okay. And you will see that, what we will study, the concepts are very similar to what we have learned in kinetic theory of gases, okay. If a charge is there stationary, there is no current motion of charge. Any guesses? Are you sure? I put a Q amount of charge here. What should come first in your mind when I am keeping charge here? A force, you need to apply some force. You need to apply some force. The basic cause of the motion of a charge there should be electric field, okay. Electrons from that side and all you should have to apply some force. It is curvature. God hasn't come and told us. Yes. I perpendicular is current density, okay. Sir, so in today actually current density. Like this, with cross section here A is suppose L, okay. So, we have found out the basic quantity. The collision. Tau G, you know Tau G. So, it should depend on factor. It's an effect micro factors.