Ohm's law for an AC circuit with a resistor, a coil and a capacitor in series
In a series circuit of a resistor R, a coil L and a capacitor C the same current flows through all elements: i = Iₘcosωt. The element voltages have different phases: in the resistor in phase with the current (U_R = Iₘ·R), in the coil leading the current by π/2 (U_L = Iₘ·X_L), in the capacitor lagging by π/2 (U_C = Iₘ·X_C). On the vector diagram U_L and U_C point in opposite directions, so the total voltage amplitude is Uₘ = √(U_R² + (U_L – U_C)²). This gives Ohm's law for the whole circuit: Iₘ = Uₘ/Z, where the impedance Z = √(R² + (X_L – X_C)²) = √(R² + (ωL – 1/(ωC))²) and X_L – X_C is the net reactance. The phase shift between voltage and current is tanφ = (X_L – X_C)/R: if X_L > X_C the voltage leads the current (inductive circuit), if X_L < X_C it lags (capacitive circuit). Energy is turned into heat only in the active resistance; in reactive elements energy is exchanged with the source. The voltage across an element can exceed the source voltage.
In your notebook draw a vector diagram to scale: the current vector on the horizontal axis, U_R along it, U_L upwards, U_C downwards. Use the values of Example 1 (U_R = 60 V, U_L = 140 V, U_C = 60 V), measure the resultant Uₘ with a ruler and compare it with the calculated 100 V.