# How to plot points on a graph curve under logarithmic coordinate axis

I am trying to draw a curve and set a special point based on the logarithmic abscissa, as shown in the following example. The function is 1/(1+(RCw)^2)^0.5.

f[w_, RC_] := 1/(1 + (RC*w)^2)^(1/2);
Manipulate[
Plot[f[w, RC], {w, 0.001  RC, 1000 RC},
AxesLabel -> {"w/RC", "|H(jw)|"},
PlotLabel -> "RC Circuit Frequency Curve",
ScalingFunctions -> {"Log", None}, PlotRange -> All,
Epilog -> {Red, PointSize[Large], Point[{1/RC, f[1/RC, RC]}],
Dashed, Line[{{1/RC, 0}, {1/RC, f[1/RC, RC]}}]}], {RC, 1, 10}]


The graph is as follows

You can see that the point (RC, 1/√ 2) is far away from its actual position(even I set point (1, 1/√ 2) like Point[{1, 1/(2^0.5)}]). How can I display the correct point? Any reply is much appreciated

• The ScalingFunctions option does not affect the Epilog option. You must explicitly take the Log in the Epilog Commented Apr 16 at 3:21
• Similar 268080
– Syed
Commented Apr 16 at 3:28

f[w_, RC_] := 1/(1 + (RC*w)^2)^(1/2);