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State the underlying principle of a pote...

State the underlying principle of a potentiometer. Why is it necessary to (i) use a long wire, (ii) have uniform area of cross-section of the wire ?

Text Solution

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Principle of potentiometer: The potential drop across the length of a steady current carrying wire of uniform cross section is proporational to the length of the wire.
(i) We use a long wire to have a lower value of potential gradient (i.e., a lower .least count. or greater sensitivity of the potentiometer.
(ii) The ara of cross section has to be uniform to get a uniform Potential gradient. as per the principle of the potentiometer.
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Knowledge Check

  • A potentiometer has uniform potential gradient. The specific resistance of the material of the potentiometer wire is 10^(-7) ohm-meter and the current passing through it is 0.1 ampere cross-section of the wire is 10^(-6)m^(2) . The potential gradient along the potentiometer wire is

    A
    `10^(-6)V//m`
    B
    `10^(-4)V//m`
    C
    `10^(-8)V//m`
    D
    `10^(-2)V//m`

  • You have two copper cables of equal length for carrying current . One of them has a single wire of area of cross- section A , the other has ten wires of cross-section (A)/(10) each . Judge their suitability for transporting a.c. and d.c.

    A
    Only single strand for d.c., either for a.c.
    B
    Either for d.c., only multiple strands for a.c.
    C
    Only single strand for a.c., either for d.c.
    D
    Only single strand for d.c., only multiple strands for a.c.

  • The current in the primary circuit of a potentiometer is 0.2A. The specific resistance and cross-section of the potentiometer wire are 4 xx 10^(-7) ohm meter and 8 xx 10^(- 7) m^(2) respectively. The potential gradient will be equal to:

    A
    1 V/m
    B
    0.5 V/m
    C
    0.1 V/m
    D
    0.2 V/m

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