USES OF POTENTIOMETER

USES OF POTENTIOMETER

Uses of potentiometer

  • Measurement of emf of cell-

 

 

 

 

POTENTIOMETER USE-1
POTENTIOMETER USE-1

Let ,

E is the  emf of  driver cell  and ,  E1  is the emf of cell to be measured

Here potential gradient K= [ {E / (R+r)} r]/l .

Let l1  is the length of the wire from zero end where galvanometer shows no deflection

Then E1 = K l1

E1 =   [ {E / (R+r)} r]/l X l1

  • Comparison of EMFs of two cells

 

 

  • POTENTIOMETER USE-1
    POTENTIOMETER USE-2

    To find the emf of two cells we connect the two cells with the potentiometer  as shown in figure  having emfs E1  and E2  .

    When 1 and 2 is connected together let null point is at length l1  from zero end,

    Then E1 = K l1 …….(i)

    Again when 2 and 3 are connected , null point  is at length  l2 from zero end ,

    Then  E2 = Kl2 ……..(ii)

    By dividing (i) and (ii) we get E1 /E2 = l1 / l2 ………..(req. equation)

    To find the internal resistance of a cell –

    POTENTIOMETER USE-3
    POTENTIOMETER USE-3

 

Let,

E – is the emf of the cell of which we have to find the internal resistance

R – is the external resistance connected with  the cell

R –  internal resistance of the cell

Let initially  switch K’ is off and l1 is the length of the null point from the zero end .

then E = K l1 ……….(i)

After that switch K’ is switched on then the null point is at l2  from zero end

then ( potential across R )       V = K l2 ……… (ii)

E/V = l1 /l2 …………..(iii)

But,  internal resistance r = [(E/V)-1] x R ……………..(iv)

So, from equation (iii) and (iv)

r =  [(l1 / l2 )-1] x R …….(req. equation)

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