9. A ring of mean radius r and cross-sectional area A is made of a perfectly conducting wire. Inductance L of the ring is so small that inertia of free electrons cannot be neglected in the current building process. The free electron density in the conductor is n, mass of an electron is m and modulus of charge on an electron is e. Initially the ring is placed in a uniform magnetic field with its plane parallel to induction vector B of the field as shown in the figure. Find the current in the ring after it is turned through an angle 90°. A: n Ae2

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