A. What is the physical significance of the fact that the voltage curve is exponentially decaying? B. Why is channel 1 menu set to AC coupling?

A. What is the physical significance of the fact that the voltage curve is exponentially decaying?

B. Why is channel 1 menu set to AC coupling?

C. If you use a constant light source instead of stroboscope which turns on and off, what do you expect to see on the oscilloscope screen?

D. If the light energy was smaller than the bandgap of silicon, will you observe the decay curve? 

These questions are all based on the  PHOTOCONDUCTIVITY OF SILICON experiment, the background information is attached.