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State working principle of potentiometer...

State working principle of potentiometer. Explain how the balance point shifts when value of resistor R increases in the circuit of potentiometer, given below.

Text Solution

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Principle of potentiometer, when a constant current flows through a wire of uniform area of cross-section, the potential drop across any length of the wire is directly proportional to the length.
Let resistance of wire AB be `R_(1)` and its length be 'I' then current drawn from driving cell -
`1 = (V)/(R+R1) " and hence"`
P.D. across the wire AB will be
`V_(AB) = 1R_(1) = (V)/(R+R1) xx (el theta)/(a)`
Where 'a' is area of cross-section of wire AB
`therefore (VAB)/(l) = (Ve)/((R+R1)a)` = constant = k
Where R increases, current and potential difference across wire AB will be decreased and hence potential gradient 'k' will also be decreased. Thus the null point or balance point will shift to right (towards, B) side.
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Knowledge Check

  • AB is wire of potentiometer with the increase in the value of resistance R, the shift in the balance point J will be

    A
    toward B
    B
    toward A
    C
    remains constant
    D
    first towards B then back towards A

  • In a potentiometer, balance point is obtained, when

    A
    the emf of the battery in the primary circuit is equal to the emf of the experimental cell in the secondary circuit.
    B
    the potential differences of the wire between the `+ve` end and jockey becomes equal to the emf of the experimental cell.
    C
    the potential difference of the wire between the `+ve` end and jockey becomes equal to the emf of the battery connected in the primary circuit.
    D
    the potential difference across the potentiometer wire becomes equal to the emf of the battery.

  • In a potentiometer of 5 wires, the balance point is obtained on the 3rd wire. To shift the balance point to the 4th wire,

    A
    current of the main circuit is to be decreased.
    B
    current of the main circuit is to be increased.
    C
    the shifting is not possible
    D
    None of the above