When a DC voltage is applied at the two ends of a circuit kept in a closed box, it is observed that the current gradually increases from zero to a certain value and then remains constant. What do you think that the circuit contains?

When a 60 mH inductor and a resistor are connected in series with an AC voltage source, the voltage leads the current by 60$$^\circ$$. If the inductor is replaced by a 0.5 $$\mu$$F capacitor, the voltage lags behind the current by 30$$^\circ$$. What is the frequency of the AC supply?

A parallel plate capacitor in series with a resistance of 100$$\Omega $$, an inductor of 20 mH and an AC voltage source of variable frequency shows resonance at a frequency of $${{1250} \over \pi }$$ Hz. If this capacitor is charged by a DC voltage source to a voltage 25 V, what amount of charge will be stored in each plate of the capacitor?

An alternating current is flowing through a series L-C-R circuit. It is found that the current reaches a value of 1 mA at both 200 Hz and 800 Hz frequency. What is the resonance frequency of the circuit?