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Read the given passage and answer the qu...

Read the given passage and answer the questions number that follow :
We know that accurate measurement of an unknown resistance can be performed on a Wheatstone bridge: However, for measuring the resistance of an ionic solution we face two problems. Firstly, passing direct current (DC) changes the composition of the solution. Secondly, a solution cannot be connected to the bridge like a metallic wire or other solid conductor. The first difficulty is resolved by using an alternating current (AC) source of power. The second problem is solved by using a specially designed vessel called conductivity cell. Basically it consists of two platinum electrodes coated with platinum black (finely divided metallic Pt is deposited on the electrodes electrochemically). These have area of cross-section equal to 'A' and are separated by distance 'l'. Therefore, solution confined between these electrodes is a column of length 'l' and area of cross-section 'A'. The resistance of such a column of solution is given by the equation :
`R = rho 1/A = 1/(kA)`
Name the instrument for accurate measurement of an unknown resistance.

Text Solution

Verified by Experts

Wheatstone bridge.
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Read the given passage and answer the questions number that follow : We know that accurate measurement of an unknown resistance can be performed on a Wheatstone bridge: However, for measuring the resistance of an ionic solution we face two problems. Firstly, passing direct current (DC) changes the composition of the solution. Secondly, a solution cannot be connected to the bridge like a metallic wire or other solid conductor. The first difficulty is resolved by using an alternating current (AC) source of power. The second problem is solved by using a specially designed vessel called conductivity cell. Basically it consists of two platinum electrodes coated with platinum black (finely divided metallic Pt is deposited on the electrodes electrochemically). These have area of cross-section equal to 'A' and are separated by distance 'l'. Therefore, solution confined between these electrodes is a column of length 'l' and area of cross-section 'A'. The resistance of such a column of solution is given by the equation : R = rho 1/A = 1/(kA) Why can't we use direct current for this measurement ?

Read the given passage and answer the questions number that follow : We know that accurate measurement of an unknown resistance can be performed on a Wheatstone bridge: However, for measuring the resistance of an ionic solution we face two problems. Firstly, passing direct current (DC) changes the composition of the solution. Secondly, a solution cannot be connected to the bridge like a metallic wire or other solid conductor. The first difficulty is resolved by using an alternating current (AC) source of power. The second problem is solved by using a specially designed vessel called conductivity cell. Basically it consists of two platinum electrodes coated with platinum black (finely divided metallic Pt is deposited on the electrodes electrochemically). These have area of cross-section equal to 'A' and are separated by distance 'l'. Therefore, solution confined between these electrodes is a column of length 'l' and area of cross-section 'A'. The resistance of such a column of solution is given by the equation : R = rho 1/A = 1/(kA) Where do we take the solution for the measurement of conductivity ?

Knowledge Check

  • Wheatstone bridge is not suitable for the measurement of resistance of the order of

    A
    ohm
    B
    kilo-ohm
    C
    mega-ohm
    D
    except (c)

  • Wheatstone Bridge is not suitable for measurement of

    A
    very high value resistances.
    B
    very low value resistances.
    C
    both (A) and (B).
    D
    medium value resistances.

  • For the accurate measurement of resistance by metre bridge, the null point should be obtained

    A
    towards left end
    B
    towards right end
    C
    at the middle of wire
    D
    all of these

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    Explore conceptually related problems

    Read the given passage and answer the questions number that follow : We know that accurate measurement of an unknown resistance can be performed on a Wheatstone bridge: However, for measuring the resistance of an ionic solution we face two problems. Firstly, passing direct current (DC) changes the composition of the solution. Secondly, a solution cannot be connected to the bridge like a metallic wire or other solid conductor. The first difficulty is resolved by using an alternating current (AC) source of power. The second problem is solved by using a specially designed vessel called conductivity cell. Basically it consists of two platinum electrodes coated with platinum black (finely divided metallic Pt is deposited on the electrodes electrochemically). These have area of cross-section equal to 'A' and are separated by distance 'l'. Therefore, solution confined between these electrodes is a column of length 'l' and area of cross-section 'A'. The resistance of such a column of solution is given by the equation : R = rho 1/A = 1/(kA) The electrical resistance of a column of 0.05 mol L NaOH solution of diameter 1 cm and length 50 cm is 5.55 x 108 ohm. Calculate its resistivity.

    Read the given passage and answer the questions number that follow : We know that accurate measurement of an unknown resistance can be performed on a Wheatstone bridge: However, for measuring the resistance of an ionic solution we face two problems. Firstly, passing direct current (DC) changes the composition of the solution. Secondly, a solution cannot be connected to the bridge like a metallic wire or other solid conductor. The first difficulty is resolved by using an alternating current (AC) source of power. The second problem is solved by using a specially designed vessel called conductivity cell. Basically it consists of two platinum electrodes coated with platinum black (finely divided metallic Pt is deposited on the electrodes electrochemically). These have area of cross-section equal to 'A' and are separated by distance 'l'. Therefore, solution confined between these electrodes is a column of length 'l' and area of cross-section 'A'. The resistance of such a column of solution is given by the equation : R = rho 1/A = 1/(kA) If the distance between the electrodes and area of cross-section of a cell are 2.5 cm and 6.75 cm^2 respectively. Calculate the cell constant.

    A meter bridge cannot be used to measure …… resistances

    Explain the use of a metre bridge for finding unknown resistance.

    What are the advantages of a Wheatstone bridge method of measuring resistance over other methods ?

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