21. State using a suitable diagram, the working principle of a moving coil galvanometer. What is the
function of a radial magnetic field and the soft iron core used in it?
For converting a galvanometer into an ammeter, a shunt resistance of small value is used in
parallel, whereas in the case of a voltmeter, a resistance of large value is used in series. Explain
why?
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Answers
Answer:
A galvanometer is an electromechanical instrument which is used for the detection of electric currents through electric circuits. It is a sensitive instrument and cannot be used for the measurement of heavy currents. It works on the principle of conversion of electrical energy into mechanical energy when a current flows in a magnetic field it experiences a magnetic torque and thus rotates through an angle proportional to the current flowing through it.
By making uniform radial magnetic field magnetic field lines are perpendicular to the magnetic moment of a galvanometer.
Soft Iron core makes the electromechanical field as radial which also increase the magnetic field.
Current Sensitivity- It is deflection produced per unit current flowing in the galvanometer.
Voltage Sensitivity- It is the minimum change in a voltage that produces an observable change in the indication or output of galvanometer.
Since Voltage sensitivity decreases with increase in resistance of the coil and the effect of an increase in the number of turns is nullified in case of voltage sensitivity so there is no change of voltage sensitivity, whenever there is a change in current sensitivity.
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