Cecil, W5DXP wrote:
"The number of joules in the stub, in both cases, is exactly the
magnitude needed to support the 100W forward wave and the 100W reflected
wave."

An energy source of frequency f feeds a 1/4-wave short-circuited stub.
The feedpoint of the stub receives a reflection from the short an
instant later which is practically equal in phase and magnitude to the
energy source.

How much energy will re-enter the source? Practically none because there
is no difference of potential between the reflection and the source.

How much energy will continue to enter the stub? Practically none
because there is no difference of potential between the source and the
reflection.

Best regards, Richard Harrison, KB5WZI