Oscilloscope amplitude reading depends on cable length? Reflection help
Here is my question, given that the source is 50 ohm terminated, will the amplitude that I measure at the scope depend on the length of the cable? ... It seems to me that the first signal will hit the scope and then reflect and this will cause the signal to double relative to the 50 ohm terminated case. however, the reflected signal travels back to the source where it is dissipated in the 50 ohm terminator which is there. So the wave doesn't bounce back multiple times. Without these multiple bounces I don't see how you can get these sort of interference affects at the oscilloscope.

This is correct. In this scenario you'll measure double the signal when the scope has a high-impedance termination, compared to if it had 50 ohm termination. This result won't depend on the length of the cable.
In the real world, the cable doesn't have exactly 50 ohm characteristic impedance and the source won't have exactly 50 ohm output impedance. Also, the cable won't be lossless. So you will see some variation in the measured amplitude, depending on the length of the cable.