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Describethe working principleof a moving coil galvanometer. Why is necessaryto use (i) a radial magnetic field and (ii) a cylinderical soft iron core in a galvanometer ? Write the expression for currentsensitivity of thegalvanometer . Can a galvanometer as such be used formeasuring the current ? Explain . |
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Answer» Solution :A moving coilgalvanometer works on the principle that when a current carrying loopor coil is placed in the uniform magneticfield, it experience a torque. (i) Radial magnetic field, produced by clindrical poles of permanentmagnet ofgalvanometeris alwaysparallelto the planeof the coil. Torqueproducedin the coil of GALVANOMETER is given by, `tau = NIABsin THETA` (ii) Cylindricalsoftiron CORE, when placed insidethe core makes teh magneticfieldstrongerand radicalbetweenit and pole pieces. Irrespectiveof position of rotationof coil, magneticfield is alwaysparallel to the plane. Current sensitivity `= (phi)/(I)= (phi(NAB))/(Kphi) = (NAB)/(K)` No , Galvanometer cannot beused formeasuringcurrent as it is very sensitive instrument,even for small value of current it gives full SCALE deflection. Galvanometercan be used in seriesconnection for measuringcurrent, it ha large resistanceso, the value of current will not be accurately measured. |
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