A diode will only allow electrons to flow in one direction.
So, one way around the diode allows a current to flow, turn the diode around and the current will not flow.
2nd year means..............engineering second year.........i know tat about diode which u mentioned........can u tell me the difference between voltage and current..........i could not understand this stuff.........
If you are in the second year of an engineering course and you dont know the difference between voltage and current, there seems to be two possibliities:
Your teacher is no good and should be sacked
or
You are totally unsuited to engineering and should find another course of study.