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Moving Coil Galvanometer, It is a device used for the detection and measurement of the currents., , In equilibrium, deflecting torque = restoring torque, , k, NBIA = kO I=——6, * “NBA, , Torsion head, , , , , , , , , , , , , , where, k = restoring torque per unit twist,, , N = number of turns in the coil,, , B = magnetic field intensity,, , A = area of cross-section of the coil and, , 0 = angle of twist., , Current Sensitivity, , The deflection produced per unit current in galvanometer is called its current sensitivity., Current sensitivity, , I,=0/1=NBA/K, , Voltage Sensitivity, , The deflection produced per unit voltage applied across the ends of galvanometer is called its, voltage sensitivity., , Voltage sensitivity, V,=0/V=NBA/KR, , where R is the resistance of the galvanometer.

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Therefore for a sensitive galvanometer, , (i) N should be large, (ii) B should be large, (iii) A should be large, (iv) K should be small, , Ammeter, , An ammeter is a low resistance galvanometer used for measuring the current in a circuit., It is always connected in series., , Conversion of a Galvanometer into an Ammeter, , A galvanometer can be converted into an ammeter by connecting a low resistance into its, parallel., , If G is the resistance of a galvanometer and it give full scale deflection for current, I, then, required low resistance S, connected in its parallel for converting it into an ammeter of range |, is given by, , s, , (I— Ig), , , , , , , , / ly, , I, x GK =(I-1,)xS, , The resistance of an ideal ammeter is zero., Voltmeter, , A voltmeter is a high resistance galvanometer used for measuring the potential difference, between two points., , It is always connected in parallel., , The resistance of an ideal voltmeter is infinity., , Conversion of a Galvanometer into a Voltmeter, , A galvanometer can be converted into a voltmeter by connecting a high resistance into its, series., , If a galvanometer of resistance G show full scale deflection for current I, then required high, resistance R, connected in series for converting it into a voltmeter of range V is given by, , V =1,(G+R), ¢ R, Ig