please help me with the output waveform of this circuit...I am confused due to presence of fifth diode..

 

The fifth diode is a Light Emitting diode (LED) drawn upside down and with the light beam missing.

 

I may be wrong,but I think it is simple diode...

Also I am sure about orientatation of diode.

 

The diode in the original circuit has reverse bias so it is doing nothing. Then the resistor in series with the diode also has no current so it also does nothing.

 

Unless its a zener for simple regulation and just has been drawn wrong.

 

@audioguru and autotuner
that's what my first reaction was ,but when I ran it in multisim the result was a rectified wave....

Thats what is confusing me...

 

and the simulation in simulink is giving me very low voltage across resistor..

So I don't know which simulation should I trust...

 

Well, if you were looking across both the diode and resistor, then there will be a rectified waveform, because the diode / resistor is basically doing nothing.
The resistor will show a small voltage across it with any diode reverse bias leakage.

 

yes,you are right....I checked the waveforms again..and it was my mistake while making oscilloscope connections....
Thanks everyone for the help