Potentiometer concept

[Scafalon40]

I don't understand how we use the potentiometer to measure the e.m.f of a cell
I've been surfing the net, all I can find are articles stating how the e.m.f is determined practically, but I haven't found sufficient theory detail.
If someone could explain it I would be grateful.

 

[CaptainDanger]

Check these :

http://physicsnet.co.uk/a-level-physics-as-a2/current-electricity/potential-divider/

http://www.cyberphysics.co.uk/topics/electricity/potentialdifference/Potential division.htm

 

[confused123]

its a device used to compare potential differences. it consists of a metre length of resistance wire stretched horizontally between two points. a driver cell is connected across the length of the wire.
Ex = AY / AB into Eo

EX being the cell of which emf is not known
AY being the jockey length connected to galvanometer, the deflection will be zero when potential difference across AY length of wire will be equal to the potential difference of driver cell.
Ab is the total length of wire which is 1 m.
Eo is the driver cell voltage.

 

[Scafalon40]

its a device used to compare potential differences. it consists of a metre length of resistance wire stretched horizontally between two points. a driver cell is connected across the length of the wire.
Ex = AY / AB into Eo

EX being the cell of which emf is not known
AY being the jockey length connected to galvanometer, the deflection will be zero when potential difference across AY length of wire will be equal to the potential difference of driver cell.
Ab is the total length of wire which is 1 m.
Eo is the driver cell voltage.

Yes yes that's all fine and good but it still doesn't explain what's happening inside the whole circuit, i.e what is the theory behind everything you stated.

 

[Scafalon40]

Check these :

http://physicsnet.co.uk/a-level-physics-as-a2/current-electricity/potential-divider/

http://www.cyberphysics.co.uk/topics/electricity/potentialdifference/Potential division.htm

Dude that's stuff on the potential divider, I need stuff on the potentiometer: specifically on how to use it to find unknown e.m.fs (the theory behind that, anyway)

 

[CaptainDanger]

Dude that's stuff on the potential divider, I need stuff on the potentiometer: specifically on how to use it to find unknown e.m.fs (the theory behind that, anyway)

Basically the same thing...
Potentiometer is used as a voltage divider...

 

[Scafalon40]

Basically the same thing...
Potentiometer is used as a voltage divider...

And what about the e.m.f part?...

 

[Scafalon40]

Does anybody know about this?
Please guys, anyone?

 

[mujtabashahnawaz]

Read the theory from Pacific Physics Volume 2. It will help you a lot

 

[Scafalon40]

Read the theory from Pacific Physics Volume 2. It will help you a lot

I don't have that one

 

[CaptainDanger]

I don't have that one

Any other book?

 

[confused123]

Yes yes that's all fine and good but it still doesn't explain what's happening inside the whole circuit, i.e what is the theory behind everything you stated.

when a potentiometer is balanced, no current flows from the cell being investigated. this means that its terminal p.d is equal to its emf. we do not have to worry about the lost volts. this is an advantage then a potentiometer has over a voltmeter which must draw a small current in order to work.
feeling better ?

 

[Scafalon40]

when a potentiometer is balanced, no current flows from the cell being investigated. this means that its terminal p.d is equal to its emf. we do not have to worry about the lost volts. this is an advantage then a potentiometer has over a voltmeter which must draw a small current in order to work.
feeling better ?

Absolutely not; you took that straight out of a book and explains nothing I don't already know.
I need stuff like "why is the current in the test cell zero.." etc

Any other book?

Quite a lot actully
Longman Advanced Level Physics
Cambridge AS and A2 Physics Coursebook
A level Physics by Nelkon and Parker
AS/A level Physics by Chris Mee and others (Hodder Education)
Notes from Tom Duncan's A level Physics( Teacher gave them to us)

 

[Scafalon40]

This is the nearest I got to an explanation:
http://www.s-cool.co.uk/a-level/phy...evise-it/using-potential-dividers-to-find-emf
Would somebody like to elaborate it please.
Bear with me guys, this is the only concept from the syllabus which I don't understand.

 

[confused123]

oh then i am sorry. i can't really go deep into this now. when you understand it share with me as well.

 

[Scafalon40]

Somebody else?
ANYBODY!
I need help

 

[mujtabashahnawaz]

Just learn the basic formula E1/E2=l1/l2 for now and look for details in book

 

[Scafalon40]

Just learn the basic formula E1/E2=l1/l2 for now and look for details in book

Know that formula.
Thank you anyway.

 

[mujtabashahnawaz]

Its an easy topic. No problem in it.Once u read it and u get all things clear. All the best

 

[thunderingthunder]

I don't understand how we use the potentiometer to measure the e.m.f of a cell
I've been surfing the net, all I can find are articles stating how the e.m.f is determined practically, but I haven't found sufficient theory detail.
If someone could explain it I would be grateful.

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.