  A well known connection between first-passage probability of random walk and
distribution of electrical potential described by Laplace equation is studied.
We simulate random walk in the plane numerically as a discrete time process
with fixed step length. We measure first-passage probability to touch the
absorbing sphere of radius $R$ in 2D. We found a regular deviation of the
first-passage probability from the exact function, which we attribute to the
finiteness of the random walk step.
