Potentiometer concept

[Scafalon40]

The use of a potentiometer is identical to that of a voltmeter and when used to measure the p.d between two points ,the terminals are connected as positive and negative terminals of a voltmeter.The sliding contact is tapped along the slide wire AB until the centre zero galvanometer is balanced. Then,e.m.f of the cell, E=p.d across the length.

Why is the current in the cell zero?

 

[thunderingthunder]

Why is the current in the cell zero?

We adjust the jockey till the galvanometer gives a reading 0.The potentiometer is connected to apply a voltage opposite to the one of the voltage you are trying to measure (the positive terminal to the positive terminal). If you adjust the voltage of the potentiometer until there is no current at all, you know that the true voltage of the battery is equal to the voltage of the potentiometer...all that with no current flowing and so no waste of energy.

 

[Scafalon40]

We adjust the jockey till the galvanometer gives a reading 0.The potentiometer is connected to apply a voltage opposite to the one of the voltage you are trying to measure (the positive terminal to the positive terminal). If you adjust the voltage of the potentiometer until there is no current at all, you know that the true voltage of the battery is equal to the voltage of the potentiometer...all that with no current flowing and so no waste of energy.

Wait...um...rephrase that please "you adjust the voltage of the potentiometer until there is no current at all"
Why so?
I'm pretty sure it's some basic concept that I'm ignoring...

 

[thunderingthunder]

Wait...um...rephrase that please "you adjust the voltage of the potentiometer until there is no current at all"
Why so?
I'm pretty sure it's some basic concept that I'm ignoring...

What you want to do is measure the voltage of the cell without actually pulling any current from it -- a so-called "no load" condition.
You can achieve this by connecting the output of the cell to a potentiometer, and then varying the potentiometer until no current flows into or out of the cell. Then, disconnect the cell and measure the voltage produced by the potentiometer.
Its not that tough..This might help you
http://books.google.com.pk/books?id=TRIA5VgModIC&pg=PA288&lpg=PA288&dq=pacific physics volume 2 potentiometer&source=bl&ots=ilSMreLmNn&sig=tdR3dwoE5-hawDS1OkjX_xIjsh0&hl=en&sa=X&ei=F-qcT5j1IISl4gTykOWpDg&ved=0CDYQ6AEwAQ#v=onepage&q&f=false

 

[Scafalon40]

What you want to do is measure the voltage of the cell without actually pulling any current from it -- a so-called "no load" condition.
You can achieve this by connecting the output of the cell to a potentiometer, and then varying the potentiometer until no current flows into or out of the cell. Then, disconnect the cell and measure the voltage produced by the potentiometer.
Its not that tough..This might help you
http://books.google.com.pk/books?id=TRIA5VgModIC&pg=PA288&lpg=PA288&dq=pacific physics volume 2 potentiometer&source=bl&ots=ilSMreLmNn&sig=tdR3dwoE5-hawDS1OkjX_xIjsh0&hl=en&sa=X&ei=F-qcT5j1IISl4gTykOWpDg&ved=0CDYQ6AEwAQ#v=onepage&q&f=false

Well it's a start
Thanks

 

[thunderingthunder]

Well it's a start
Thanks

np