the question asks you to calculate the standard derivation for the mean distance of an electron from the nucleus.
you are given the mean distance (<r>), and the probability density
delta r = sqrt (<r^2> - <r>^2)
<r> = 3.a/2
The Attempt at a Solution
We had to calculate <r^2> by integrating a given value.
after integrating by parts 4 times i ended up with -3a^2
putting this into the standard derivation lead to the square root of minus 21.a^2/4
this obviously gives a complex value.
i was wondering if this can be correct, or if the negative sign has no meaning in the calculation.
i have read from some physics books but i cant find an answer