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Grade: 11


In the circuit, voltameter is ideal and its least count is 0.1 V (Whats least count?) The ammeter is 1 mA. Let reading of voltameter be 30.0 V and the reading of ammeter is 0.020 A. Calculate the value of resistance R with error limits.

11 years ago

Answers : (1)

Ramesh V
70 Points

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 = 10-3

  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

11 years ago
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