Class 12th Physics 2017 Set3 Delhi Board Paper Solution
Describe the working principle of a moving coil galvanometer. Why is it necessary to use (i) a radial magnetic field and (ii) a cylindrical soft iron core in a galvanometer? Write the expression for current sensitivity of the galvanometer. Can a galvanometer as such be used for measuring the current? Explain.
A moving coil galvanometer works on the principle that when a current carrying loop or coil is plcaed in the uniform magnetic field, it experiences a torque.
(i) A radial magnetic field, produced by cylendrical poles of permanent magnet of galvanometer is always parallel to the place of the coil. Torque produced in the coil of galvanometer is given by ,
(ii) Cylindrical soft iron core, when placed inside the core makes the magnetic field stronger and radical between it and pole pieces. Irrespective of position of rotation of coil, magnetic field is always parallel to the plane.
Current sensitivity = φ / I = φ(NAB) / Kφ = NAB / K
No, galvanometer cann't be used for measuring current as it is very sensitive instrument, even for small value of current it gives full scale deflection.
Galvanometer can be used in series connection for measuring current, it has large resistance. So, the value of current will not be accurately measured.
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