A diode as two posts anode and cathode (anode more positive then negative, cathode more negative then positive) and electrically can only flow one way inside a diode. the way to tell between A and K is by looking for a stripe on the diode and that should be the cathode and on a l.e.d type diode the longer metal leg is the anode. that's so you don't set it up the wrong way. the way to check if you've set it up the wrong way just do a test with the multimeter and if you have set it up reverse biased direction you shouldn't get a reading something like 0.00v,(got this little diagrams form google to show things bit more clear)
then i built a little circuit with a resistor diode and/or l.e.d 1st using a multimeter I found out witch how to tell the difference between anode and cathode one both l.e.d and/or a diode..when i measured the l.e.d in forwards biased i got a reading of 1.796V when i measured the diode i got a reading of .544V, when i measured both of them in reverse biased i got a reading of 0.00V. which means that a diode and/or a l.e.d will not work in reverse biased. we also had to identify which leg is the anode and cathode on the both l.ed or diode,on the diode it was easy there was a tripe on it and that is the cathode and one the l.e.d the longer metal leg is the anodethen i built a little circuit with a resistor diode and l.e.d
did some calculation using ohs law(A = V/R )
VS=5V,R=1KOHMS=1N4007
5V-.6/1K= .0044A
Then we calculate and measured few things to check our a answers useing this formula
V = I x R =(VS-VD) / R
these brackets are showing they must be caculated first
and for a 1 K resistor the didoe needs value of 1000v to operate in safe region.
i replaced the diode by an l.e.d and calculate the current by useing ohms law.
VS - VD = X/R = I
5 - 1.75 = 3.3/1K = 0.32MA
