if we connect ldr to one of analog input pin.does the change in resistance converted to digital value or the voltage which changes by potential divider circuit converted to digital value or niether.

 

"Analog" may mean the pin connects to an "analog to digital converter." These A2D converters act like simple voltmeters, so they will sense " the voltage which changes by potential divider circuit" and convert that to a digital value.

If you correctly scale the divider you may get a useful conversion.

 

1)i have connected 3v dc supply ldr ant led in series

2)i have connected 3v dc supply with potential divider circuit by resistor and ldr and connected it to led

the second works good.does first one works

 

u should be more specif.
What you said does not make any sense wht's so ever.

 

1)i have connected 3v dc supply ldr ant led in series

2)i have connected 3v dc supply with potential divider circuit by resistor and ldr and connected it to led

the second works good.does first one works

If you would post a schematic, more people could understand your question, and you would get better answers.

 

i have no simulation software so i did it in paint

is that right way of connecting

 

show wht u drew !!

 

You also have a thread going on here http://forum.allaboutcircuits.com/showthread.php?t=93090 With almost the exact same question. I would not say it is site rule violation. But it is very confusing for other to help then you work this way. Then you create a thread in this forum. You are the owner of this thread. And you are free to take in any direction you want. So it would be perfectly OK. To start a thread asking on how to use a LDR, and then widen the topic some. And ask for help to connect this setup to micro in the same thread

 

http://postimg.org/image/thcewcwot/

 

Keep discussion on the same topic in one thread.
I have merged the two threads into one.

 

http://bildr.org/2012/11/photoresistor-arduino/