Which sources produce alternating current?

Which source produce alternating current ?

A bulb and a capacitor are connected in series to a source of alternating current. If its frequency is increased, while keeping the voltage of the source constant, then

An LCR circuit is connected to a source of alternating current. At resonance, the applied voltage and the current flowing through the circuit will have a phase difference of

An LCR circuit is connected to a source of alternating current. At resonance, the applied voltage and the current flowing through the circuit will have a phase difference of

A resistance of 20 ohm is connected to a source of alternating current rated 110 V - 50 Hz. Find the r.m.s of current.

A resistance of 20 ohm is connected to a source of alternating current rated 110 V - 50 Hz. Find the maximum instantaneous current in the resistor.

Which device produces an electric current ?