I have a homework assignment question on accretions discs (essentially an estimation of the number of electron scatterings, but this is just for background).
There are a few parameters, one of them being $L$, which is the linear size of the medium (the medium in this case being an accretion disc around a blackhole)
Now, I have been given the mass of the black hole. Other than that, nothing else which could give me the linear size of the accretion disc.
Could I assume that the linear extent of the accretion disc is perhaps of the order of a few Schwarzschild radii? Which could be calculated from the mass, which is given.
If anyone could shed some light on this I would be very appreciative. I need a nudge in the right direction on this.