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