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**dd** on
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A coil consists of N=105 turns of wire wrapped uniformly around a plastic torus. The inside radius of the torus is r0=0.12 m and the outer radius is r1=0.14 m. Thus, each winding has a diameter d=0.02 m. What is the self-inductance (in H) of this coil? Work in the approximation d≪r0.