15. A long solenoid of radius r having n turns per unit length carries a constant current I. Consider two situations, in the first an inertia-less paper cylinder of radius r, (rp < r) and length l is inserted coaxially at the middle of the solenoid and in the second case another inertia-less paper cylinder of radius rp (r, > r) and length I surrounds coaxially the solenoid in the middle as shown in the figures. The paper cylinders carry uniform charge Q over their curved surfaces. If current in the solenoid 1s suddenly reduced to Iln, find angular velocity w acquired by the paper cylinders. Ignore effects of gravity. 2an IL(2-1) →pく 7ト>8

15. A long solenoid of radius r having n turns per unit length carries a constant current I. Consider two situations, in the first an inertia-less paper cylinder of radius r, (rp < r) and length l is inserted coaxially at the middle of the solenoid and in the second case another inertia-less paper cylinder of radius rp (r, > r) and length I surrounds coaxially the solenoid in the middle as shown in the figures. The paper cylinders carry uniform charge Q over their curved surfaces. If current in the solenoid 1s suddenly reduced to Iln, find angular velocity w acquired by the paper cylinders. Ignore effects of gravity. 2an IL(2-1) →pく 7ト>8