Question

Which among the following statements is wrong:
(A) when all resistance are equal, then the sensitivity of a wheat-stone bridge is maximum
(B) when the galvanometer and the cell are interchanged, then the balancing of the wheat-stone bridge will be affected
(C) Kirchoff’s first law for the currents meeting at the junctions in an electric circuit shows the conservation of charge
(D) Rheostat can be used as potential divider

Answer 1

We will check for all the options in our problem and see which of them are correct and which of these are incorrect with the help of their respective properties. Doing so will give us the required solution, that is, which of these option(s) is/are incorrect in their respective domain and why.

Complete answer:
Let us analyze all the statements one by one.
(A) When all resistance are equal, then the sensitivity of a wheat-stone bridge is maximum: It is defined as deflection in galvanometer per unit fractional change in the unknown resistance. When all the resistances are equal this fractional change is zero, and hence the sensitivity is maximum. Hence, this option is correct.
(B) When the galvanometer and the cell are interchanged, then the balancing of the wheat-stone bridge will be affected: the condition of wheatstone bridge depends on the four resistors alone and not the connection. Hence, when galvanometer and cell are interchanged, balancing will not be affected. Hence, this option is incorrect.
(C) Kirchoff’s first law for the currents meeting at the junctions in an electric circuit shows the conservation of charge: it states that the influx of current is equal to the out-flux of current. This is constant at all the times at all the junctions. Hence, this means it is derived from the concept of conservation of charge. Hence, this option is also correct.
(D) Rheostat can be used as a potential divider: Since, potentiometer is a three-terminal resistor, rheostat can be used in its place as a two-terminal resistor. Hence, this option is also correct.
Hence, from our observation the only statement not true is (B).

So, the correct answer is “Option B”.

Note: We should always use the practical workings of all the instruments and devices used in our conceptual problems. These not only form a good set of questions but also enhance our ideas on how to use them in practice and will be of great help while performing various experiments during our higher studies.