[Physics] Why the bulb does not glow in this configuration of batteries

batterieselectric-circuitselectricity

I connected a bulb to a battery positive terminals with positive and negative terminals with negative .
It glows as it should but when i connect the positive terminal of the same bulb to the positive terminal of one battery and negative terminal of the same bulb to the negative terminal of another battery. The bulb does not glow.

Bulbs

What I want to ask here is that electric potential difference is being maintained then why does the bulb does not glow.
NOTE : Batteries are not connected with each other. Both batteries are separately placed.

Best Answer

The potential difference exists between the two plates of the same battery. You don't know for sure if the potential difference exists between two plates from different batteries.

Additionally, you're not allowing any current to flow even if there is some potential difference. In other words, you have not closed the circuit. Current can't flow in a circuit that's not closed.