When the frequency of the applied voltage increases in a series RL circuit:

Concept:

The impedance of the series RL circuit opposes the flow of alternating current.

The impedance of a series RL Circuit is nothing but the combined effect of resistance (R) and inductive reactance (XL) i.e ωL of the circuit as a whole.

The impedance Zeq in ohms is given by,

Zeq = √(R2+XL2)

Analysis:

If;

Frequency (f) of applied voltage increases → ω ↑  → XL ↑ → Zeq ↑ 

As the value of reactance increases, the phase angle also increases.