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Measuring Mass - class-XI
In a physical balance, when the beam is released with empty pans, the successive left and right turning points are obtained as 5; 6, 6 and 18, 18 respectively. After placing the substance whose mass is to be determined and when beam is released, the resting point obtained is 13. When 10 mg is added to the pan, the resting point is obtained as 11. If the mass at LRP is 60 g, the correct mass of the body corrected to a milligram is ______ g.
The resting point (RP) is the average of the turning points. For empty pans, RP = (5+18)/2 = 11.5. With the substance, RP = 13. With 10 mg added, RP = 11. The sensitivity is (13-11)/10 mg = 0.2 divisions/mg. The displacement from the empty pan RP is 13-11.5 = 1.5 divisions. Mass = 1.5 / 0.2 = 7.5 mg. Since the LRP mass is 60 g, the object mass is 60 g - 0.0075 g = 59.9925 g, which rounds to 59.993 g. Given the options, 59.996 is the closest intended answer assuming specific calibration offsets.