A long solenoid has 70 turns / cm and carries current $I$. An electron moves within the solenoid in a circle of radius 2.5 cm perpendicular to the solenoid axis. If the speed of the electron is $4.4 \times 10^6 \mathrm{~m} / \mathrm{s}$, then the current $I$ in the solenoid is
(take $\mu_0=4 \pi \times 10^{-7}$ Si unit, mass electron $=9 \times 10^{-31}$
kg , charge of electron $1.6 \times 10^{-19} \mathrm{C}$ )
A flat circular coil has 100 turns of wire of radius 10 cm . A uniform magnetic field exists in a direction perpendicular to the plane of the coil and it grows at a rate of $0.1 \mathrm{~T} / \mathrm{s}$. The induced emf in the coil is
A $2 \mu \mathrm{~F}$ capacitor is charged to 50 V by a battery. The battery is removed after capacitor if fully charged. At time $t=0$, a 10 mH coil is connected in series with the capacitor. The maximum rate at which the current changes in the circuit is
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