Why Does a Galvanometer Show Zero Deflection Despite Potential Differences?

[abhijit.k939]

Potentiometer conceptual help!

The book that i am using currently states that "If the potential difference between A and J is equal to the emf of the cell, no current flows through the galvanometer. It shows zero deflection."
But suppose A be at 10V and J at 5V, and The +ve terminal of battery at 5V and negative at 0V
Therefore the Potential Difference between AJ and the emf of cell are same ,
but the pottential difference between A and +ve terminal of cell is 5V so current should flow, same for J and -ve terminal.So there should be deflection in galvanometer due to flow of current.Then why not?

Note: A and J are connected to the driving circuit as well as the battery to be measured

I wasnt able to post link for the image directly
http:+//tinypic.com+/r/4kw+7yx/6 (Remove all the + signs)

 

[the_emi_guy]

abhijit.k939
It looks from your schematic that node A and the +ve terminal of the battery are the same node. This would prohibit them from being at different voltages.