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(a) The torque acting on the coil of moving coil galvanometre is <br> `tau=NiAB` <br> Given `tau=ki` <br> `ki=NiAB implies k=NBA` <br> (b) If C is torsional constant of the spring of galvanometre, then <br> `tau=C theta` <br> `Ni_0AB=C(pi/2) implies C=(2NBAi_0)/pi` <br> (c) If `q_m` is the maximum deflection, then from conservation of energy <br> `1/2C theta^_m^2=1/2Iomega^2 implies theta_m=sqrt(I/C) omega`.....(i) <br> we have `tau=NiAB` Put `tau=(dL)/(dt)` where `L` is angular momentum. <br> `(dL)/(dt)=N((dQ)/(dt))AB` or `dL=NABdQ` <br> Integrating `int_0^LdL=NABint_0^QdQ implies L=NABQ` <br> If `omega` is angular velocity, <br> Put `L=Iomega` <br> `Iomega=NABQ` <br> `omega=(NABQ)/I....(ii)` <br> Subtituting this value in Eq. (i), we get <br> `theta=sqrt(I/C). (NABQ)/I=(NBAQ)/({sqrt((2NABi_0I)/pi)}) =Qsqrt((piNAB)/(2Ii_0))`.