question_answer 55)

  A multi range current meter can be constructed by using a galvanometer circuit as shown in Fig. 3(EP).10. We want a current meter that can measure 10 mA, 100 mA and 1 A using a galvanometer of resistance 10  and that produces maximum deflection for current of 1 mA. Find  that have to be used.

Answer:

                  Here, G = 10, = 1 mA = A. To convert a galvanometer into an ammeter of given range of current 0 to , the shunt resistance required is  . Case (i), = 10 mA = 10 x A, .          ?.. Case (ii), When  galvanometer resistance =        ?.. Case (iii), When galvanometer resistance =                ?.. Putting the value of  in , we get From ,       ?.. From , or                                        ?.. Subtracting  from , we get, or    From ,