Q21 of 30 Page 1

Answer the following:

(a) Why are the connections between the resistors in a meter bridge made of thick copper strips?


(b) Why is it generally preferred to obtain the balance point in the middle of the meter bridge wire?


(c) Which material is used for the meter bridge wire and why?


OR


A resistance of R Ω draws current from a potentiometer, as shown in the figure. The potentiometer has a total resistance Ro Ω. A voltage V is supplied to the potentiometer. Derive an expression for the voltage across R when the sliding contact is in the middle of the potentiometer.


(a) The connections between the resistors in a meter bridge are made of thick copper strips because the resistivity of the copper wire is very low. As, the connections are thick, so the area become very large and the resistance of eh wires become almost negligible.


(b) It is preferred to obtain the balance point in the middle of the meter bridge so as to increase the sensitivity of the meter bridge.


(c) Constantan (a nickel-copper alloy) is used to make the wire of the meter bridge as its temperature coefficient is almost negligible due to which the resistance of the wire does not get affected on increasing the temperature of the wire due to flow of current for long time during the experiment.


OR


When the slider is in the middle the resistance of each part becomes R0/2


The resistance of the parallel combination of R and R0/2 is,


Hence the total resistance R will be given by the following



We get



The equivalent resistance of the circuit becomes,





The net current in the circuit is,



Voltage across R is,




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