QUESTIONS FOR SHORT ANSWER

When the frequency of the AC source in an LCR circuit equals the resonant frequency, the reactance of the circuit is zero. Does it mean that there is no current through the inductor or the capacitor? 

When an AC source is connected to a capacitor, there is a steady-state current in the circuit. Does it mean that the charges jump from one plate to the other to complete the circuit? 

A current $i_1=i_0\sin \text{ω}t$ passes through a resistor of resistance $R$. How much thermal energy is produced in one time period ? A current $i_2=-i_0 \sin \text{ω}t$ passes through the resistor. How much thermal energy is produced in one time period? If $i_1$ and $i_2$ both pass through the resistor simultaneously, how much thermal energy is produced? Is the principle of superposition obeyed in this case? 

Is energy produced when a transformer steps up the voltage?

A transformer is designed to convert an $AC$  voltage of $220 \mathrm{V}$ to an $AC$ voltage of $12 \mathrm{V}$. If the input terminals are connected to a $DC$ voltage of $220 \mathrm{V}$, the transformer usually burns. Explain. 

Can you have an $AC$ series circuit in which there is a phase difference of (a) $180°$, (b) $120°$ between the emf and the current? 

A resistance is connected to an $AC$  source. If a capacitor is included in the series circuit, will the average power absorbed by the resistance increase or decrease? If an inductor of small inductance is also included in the series circuit, will the average power absorbed increase or decrease further? 

Can a hot wire ammeter be used to measure a direct current having a constant value? Do we have to change the graduations?