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Blazing goIITian

Joined:	5 Nov 2007
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10 Oct 2008 14:00:20 IST

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Potentiometer conceptual doubt

Engineering Entrance , Medical Entrance , AIPMT , JEE Main , AIIMS , JEE Advanced , Physics , Electricity

The given figure represents a potentiometer with balance point at X.

What will happen to balance point if :

a) R is increased?

b) S is increased?

c) P is replaced by a cell with lower emf than Q?

Please give the entire explanation, especially for a) and b).

Thanks!:-)

Rates assured!

Comments (6)

HEMANT BHARDWAJ

Blazing goIITian

Joined: 6 Apr 2007

Posts: 851

10 Oct 2008 18:26:08 IST

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A-

if R is increased then the value of current flowing in potential metre shouid decrease which will result in lower value of potential gradient(drop of potential per unit length)

Hence to re-establish balance point u wouid require to shift the point X to right(i.e toward"s point B)

i m giving here some more explanation

initially when the resistance was R then balance point was at X suppose AX=L since potential metre is balanced at this position which mean potential difference b\w A and X is equal to EMF of cell Q(EMF coz no current is flowing through Q hence no potential drop when potential metre is balanced)

Next suppose u increased the resistance which will result decrease in value of current in potential metre so for producing same potential drop=EMF of cell Q u hav to shift the balance point toward"s B..

HEMANT BHARDWAJ

Blazing goIITian

Joined: 6 Apr 2007

Posts: 851

10 Oct 2008 18:32:12 IST

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B-

As no current flows through galvanometre, cell Q , or resistance S when potential metre is at balanced position.

Hence there will be no effect of decreasing\increasing value of S..

HEMANT BHARDWAJ

Blazing goIITian

Joined: 6 Apr 2007

Posts: 851

10 Oct 2008 18:48:04 IST

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if P is replaced by a cell with lower emf than Q then u can not achieve balance point.

now u can think y not............

Learner .

Blazing goIITian

Joined: 5 Nov 2007

Posts: 507

11 Oct 2008 00:00:41 IST

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Is it because the arm has very low pd across it, but the jockey is connected to high pd and so they can't balance each other?

Thanks a lot for the answers- the first one is now clear. But the answer to b) says that it will shift to the left.

Is the book answer wrong?

aditya

New kid on the Block

Joined: 1 Sep 2008

Posts: 6

11 Oct 2008 13:54:51 IST

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if we increase the resistance S then the potential difference across point A and point X will decrease and so we have to shift the jockey towards left to make the potential difference of the potentiometer cell and the cell which we have attached thereby getting a null deflection point

HEMANT BHARDWAJ

Blazing goIITian

Joined: 6 Apr 2007

Posts: 851

11 Oct 2008 14:16:59 IST

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ya surely answer of b is wrong in book if it is what u r saying.

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Comments (6)

A-

if R is increased then the value of current flowing in potential metre shouid decrease which will result in lower value of potential gradient(drop of potential per unit length)Hence to re-establish balance point u wouid require to shift the point X to right(i.e toward"s point B)

Next suppose u increased the resistance which will result decrease in value of current in potential metre so for producing same potential drop=EMF of cell Q u hav to shift the balance point toward"s B..

B-As no current flows through galvanometre, cell Q , or resistance S when potential metre is at balanced position.Hence there will be no effect of decreasing\increasing value of S..

if P is replaced by a cell with lower emf than Q then u can not achieve balance point.now u can think y not............

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if R is increased then the value of current flowing in potential metre shouid decrease which will result in lower value of potential gradient(drop of potential per unit length)

Hence to re-establish balance point u wouid require to shift the point X to right(i.e toward"s point B)

B-

As no current flows through galvanometre, cell Q , or resistance S when potential metre is at balanced position.

Hence there will be no effect of decreasing\increasing value of S..

if P is replaced by a cell with lower emf than Q then u can not achieve balance point.

now u can think y not............