The least count(L.C) of any measuring equipment is the smallest quantity that can be measured accurately using that instrument.Thus Least Count indicates the degree of accuracy of measurement that can be achieved by the measuring instrument.

Given,  L.C of Ammeter is     1mA

             L.C of Voltameter is   0.1V

Always an Ammeter is connected in-series- with circuit  to measure electri current through it  and

Voltmeter is connected in parallel to measure voltage across its ends.

OHMs law expression is : V=IR (or)    R=V / I       

Here given I = 0.02A , V = 30V ,dV = 0.1V , dI = 10^-3A 

  so, R = 30 / 0.02 =1500 ohms

                                            ln R = ln V + ln I

                                            dR/R = dV/V + dI/I

                                             dR = R*(dV/V + dI/I )

                                                   =1500*(0.1/30 + 0.001/0.02)

                                                   = 80 ohms

        Resistence with error limits = ( 1500 ± 80 ) ohms

and % error in resistance is = 5.33%

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Naga Ramesh
IIT Kgp - 2005 batch