In an AC circuit, resistance 50 Ω, inductance 0.3 H and capacitance 15 μF is connected to an AC voltage source 25 V, 50 Hz. Determine the phase difference between current and voltage.

Kirchhoff's laws for AC circuits are:
The phasor sum of the currents at any point in the circuit is zero.
The phasor sum of the voltages around any closed loop is zero. 

Kirchhoff's laws can help calculate the electrical resistance of a complex network, or impedance in the case of alternating current. 
Kirchhoff's current law (KCL) states that the algebraic sum of branch currents flowing into and out of a node is equal to zero. This is a result of the principle of the conservation of electric charge. 
Kirchhoff's laws for AC circuits are derived in the same way as those for DC circuits