A circular coil of wire of radius $$r$$ has $$n$$ turns and carries a current $$I$$. The magnetic induction $$B$$ at a point on the axis of the coil at a distance $$\sqrt{3} r$$ from its centre is
If voltage across a bulb rated $$220 \mathrm{~V}, 100 \mathrm{~W}$$ drops by $$2.5 \%$$ of its rated value, then the percentage of the rated value by which the power would decrease is
A long solenoid has 500 turns, when a current of $$2 \mathrm{~A}$$ is passed through it, the resulting magnetic flux linked with each turn of the solenoid is $$4 \times 10^{-3} \mathrm{~Wb}$$, then self induction of the solenoid is
A fully charged capacitor $$C$$ with initial charge $$q_0$$ is connected to a coil of self inductance $$L$$ at $$t=0$$. The time at which the energy is stored equally between the electric and the magnetic field is