(a) →τ=→M×→B, M=NiA
τ=ki=BiNA
k=BNA
(b) τ=KΘ=BiNA (K is torsional constant)
K=2BiNAπ[∵Θ=π2]
(c) τ=BiNA
∫t0τdt=∫t0BNAidt
I0=BNAQ
I0=BANQI
12Io)2=12KΘ2 [At maximum deflection whole K.E. will convert in to potential energy of spring]
Θ=√Io)2K=BANQI√2BiNAIπ
Θmax=Q√BNAπ2I.