Application of potentiometer

(A) Comparison of EMF's of two cells using potentiometer

  • Consider the circuit arrangement of potentiometer given below used for comparison of emf's of two cells

    Application of potentiometer

  • Positive terminals of two cells of emf's E1 and E2( whose emf are to be compared ) are connected to the terminals A and negative terminals are connected to jockey through a two way key K2 and a galvanometer
  • Now first key K1 is closed to establish a potential difference between the terminals A and B then by closing key Ksub>2 introduce cell of EMF E1 in the circuit and null point junction J1 is dtermined with the help of jockey.If the null point on wire is at length
    l1 from A then
    Where K -> Potential gradient along the length of wire
  • Similarly cell having emf E2 is introduced in the circuit and again null point J2 is determined .If length of this null point from
    A is l2 then
    This simple relation allows us to find the ratio of E1/E2
  • if the EMF of one cell is known then the EMF of other cell can be known easily

(B) Determination of internal resistance of the cell