A microammeter has as resistance of `100 Omega` and full scale range of `50 muA`. It can be used a voltmeter or as ahigher range ammeter provided a resistance is added to it. Pick the correct range and resistance combinations
50 V range with `10 kOmega` resistance in series
b.`10 V` range with `200 kOmega` resistance in series
c. 5mA rangw with `1Omega` resistance in parallel
`10 mA` range with `1Omega` resistance in parallel

Options

A. (i),(ii)
B. (ii),(iii)
C. (iii),(iv)
D. all

Answer

B

Explanation

`G = 100 Omega, i_g = 50 mu A`
(i) `V = i_g (R + G)`
`50 = 50 xx 10^-6 (R + 100) rArr R = (10^6 - 100)ohm`
(ii) `(10 = 50 xx 10^-6)(R + 100) rArr R = (2 xx 10^5 - 100) Omega, O.K`.
(iii) `(i-i_g) S = i_g G`
`(5 xx 10^-3 - 50 xx 10^-6) S = 50 xx 10^-6 xx 100`
`S = (1)/(1 - 0.01) = 1.01 Omega, O.K`
(iv) `(10 xx 10^-3 - 50 xx 10^-6) S = 50 xx 10^-6 xx 100`
`(10 - 50 xx 10^-3) S = 5`
`S = (5)/(10 - 0.05) = 0.5 Omega`.