POTENTIOMETER

THIS TOPIC EXPLAIN ABOUT THE POTENTIOMETER

 Potentiometer – An instrument used to measure accurately the EMF or potential difference is called potentiometer.

Principle– Its working based on the principle that the potential drop across a conductor is directly proportional to the length of the conductor , if constant current passes through the conductor having uniform area of cross-section .

Construction –

 

As we know ,

potential V=IR

V = (ρl/A) I

Since current is constant and area of cross-section is uniform  so V α l

Or V = K l

K = V/l ( K is a constant called potential gradient)

[ calculation of potential gradient ( students don’t have to derive it in case of potentiometer it is useful for the numerical questions) – if Rh = r and resistance of the wire is r and E is the emf of  driver cell  then ,  current through the circuit is , i = E/ (R+r)

There fore potential difference at the end  the wire is v= i r

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

Potantiometer is preferred over the galvenometer to measure  potential difference across a conductor