Experimental Skills (Physics) · Question 3

Two thin wires, Wire-1 of diameter 0.650 mm and Wire-2 of unknown diameter d are given. To obtain the value of d, the diameters of the two wires are measured with a screw gauge. The screw gauge has a pitch of 0.5 mm and there are 100 divisions on the circular scale (CS). The smallest division on the linear scale (LS) is 0.5 mm. The table shows the readings of LS and CS for the measurements. The value of d (in m) is: array|c|c|c| & 2c|Readings \ 2-3 & LS (mm) & CS \ Wire-1 & 0.5 & 42 \ Wire-2 & 1.5 & 95 \ array

As shown in the figure, the resistance of a galvanometer G can be found by the half-deflection method. Here the resistance R2 is adjusted such that when the key K is closed the deflection in the galvanometer becomes half of the value as compared to when K is open. Half-deflection is obtained at R2=4 and thus the galvanometer resistance is found to be 6 . In this half-deflection condition the current (in mA) through the resistor R1 is: [figure]