in moving coil galvanometer, the coil is wound over the mettalic frame in order to make the galvanometer dead beat i.e. on passing current the galvanometer shows a steady deflection without any oscillation.what does dead beat mean? how is the use of mettalic frame related to this?

Dear student,

When a current is passed through the coil in the direction PQRS, then the coil experiences a torque

t = NIBA sina

Since the magnified field is radial the plane of the coil is parallel to the magnetic field such that a = 90^o and hence t = NIBA.

The coil rotates and the phosphor bronze strip gets twisted. As a result a restoring torque comes into play trying to restore the coil back to original position.

If f be the twist produced in the strip and C be the restoring torque per unit twist then the restoring torque = Cf.

In equilibrium,

where G is the galvanometer constant.

Please feel free to ask your queries here. We are all IITians and here to help you in your IIT JEE preparation.

All the best.

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