Voltage Noise Density of Resistor

[vim831]

Hello,

I want to gain a proper understanding of what thermal noise in a resistor really is. I have a basic understanding but i was hoping someone could explain it in better detail.

Yes, this is a homework question, however I really want to understand this more than I want to get the answer correct. My current solution is attached.

V = sqrt (4kTBR) explain what this equation means and how it is derived.

Thanks.