✔ 最佳答案
As you didn't describe how the experiment is performed, I could only give two general reasons.
(i) The capacitance is not fully charged or fully discharged during a cycle. As such, the actual current so measured is smaller than the expected current. When a plot of frequency f against the discharge current I is done, the plotted line would be shifted somehow.
(ii) There is leakage current in the capacitor. Again, this leads to the fact that the charged stored in the capacitor is less than what is expected. Thus, the discharge current is smaller than the expected current. This would shift the plotted line from the origin.