A micro-ammeter has a resistance of 100 Ohm anf full scale range of 50micro Ampere. It can be used as a voltmeter and an ammeter of a higher range provided a resistance is added to it. Pick the correct range and resistance combination(s) :-

(A) 50 V range & 10 kilo Ohm resistance in series

(B) 10 V range & 200 kilo Ohm resistance in series

(C) 5 mili ampere with 1 ohm resistance in parallel

(D) 10 mili ampere range with 1 Ohm in parallel

the voltage is given as

V = Ig(G + S)

where

Ig = 50uA = 50 x 10-6 A

G = 100 ohms

S = 200 Kilohms = 200000 ohms

so,

V = 50 x 10-6 x (100 + 200000)

or

V = 10V

.

and

current is given as

I = ((G + S) / S).Ig

so,

here S = 1 ohms

this,

I = ((100 + 1) / 1).50 x 10-6

so,

I = 5 x 10-3 A  = 5mA

so,

form the above two sets of values we infer that options (b) and (c) are correct, respectively.

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