An oscilloscope shows a steady sinusoidal signal of 5 volt peak to peak, which spans 5 cm in vertical direction on the screen. by tweaking the time sweep, the periodic saw-tooth voltage of the oscilloscope is replaced by voltage signal identical to the one that is detected. what will be observed on the oscilloscope screen? 2. on a 20 mhz oscilloscope as those used in class, the knob of the time sweep rate shows for the fastest setting the mark of 0.2 microseconds per major division in horizontal direction on the screen. how many full periods of a 5 mhz periodic signal will be observed in one major horizontal division?

There is some confusion in the phrase, "By tweaking the time sweep, the periodic saw-tooth voltage of the oscilloscope is replaced. . ." 

I assume this means that, instead of using the time base saw tooth to drive the horizontal deflection, you use an external sinusoidal input signal to drive the horizontal deflection. If I am correct about this, then it is a very poorly worded question, and the result would be a diagonal line on the screen, since, at every moment, the vertical deflection would coincide with a proportional horizontal deflection. I think the external horizontal input deflects to the right, for a positive voltage, so the diagonal would by low on the left and high on the right. 

If the horizontal amplifier was set to the same deflection sensitivity as the vertical input amplifier, the diagonal would have a slope of 45 degrees.