connecting two common ground on the breadboard to one on arduino?

Since i am a newbie,i have a problem regarding joining two common ground on the board.In this case the first led is connected to ground and some pin no. but the 2nd and third led,their anodes are connected to the pin nos. on the arduino board but their cathode is just left on the ground rail on the breadboard.What i am confused is can we connect these two ground from 2nd and 3rd led with the 1st led?

All grounds should be connected.

To start with, draw a schematic diagram of the circuit you are talking about. This helps to visualize whats happening.

For review: Light Emitting Diodes (LEDs) &
Circuit Symbols of Electronic Components

Great Links... Both good stuff.

Bob

codlink: All grounds should be connected.

No, all grounds MUST be connected.

fungus: No, all grounds MUST be connected.

lol, true, but can think of instances where you shouldn't, but that's for another discussion..

Like Larry said, we need a schematic of your setup to help in more detail.

here ground fromarduino is not connected with the grounds from two leds…

I am having some trouble understanding.
The cathodes of all the LEDS can share a common ground point on a breadboard.

Ground.jpg

Even without connecting common ground it worked and i am wondering how this circuit worked!!!Having problem in it....

A4kash: Even without connecting common ground it worked and i am wondering how this circuit worked!!!Having problem in it....

Grab a multimeter and you can measure the difference between the grounds. Maybe you got lucky and it wasn't enough difference to burn out your LEDs or Arduino.

But don't depend on it. One day the magic smoke WILL come out of your components if you don't use common ground.

And this one didn’t even worked at all…

and this was the circuit…

t1.jpg