[Phys-L] Johnson noise i.e. thermal noise in resistors

[John Denker <jsd@av8n.com>]

We take the Johnson noise (i.e. the Nyquist formula)
as a given, so we know the amount of noise produced by
a given resistor.

    ⟨V^2⟩ = 4 kT B R                     [1]

A) Just for fun:  That's for a single resistor.
 Now Sppose we have two resistors in parallel.
 How much noise is produced by the combination?





As usual, I have an ulterior motive.  Therefore:

B) What makes question (A) worth asking?  What makes it
 interesting and amusing?


Spoiler:  My answer:
  https://www.av8n.com/physics/johnson-noise.htm
or equivalently:
  http://www.av8n.com/physics/johnson-noise.htm


Note that algebraically, equation [1] could hardly 
be simpler, although conceptually you have to think 
about it for a while before you really understand it.