Let us consider an AC series LCR circuit of angular frequency ω . The impedance of the circuit is given by,Z=R2+(ωL−ωC1​)2​ The phase difference between V and / is given by,tanϕ=(ZωL−ωC1​​) From the above formula, we can clearly see thatϕ∈(−2π​,2π​) So, we cannot have a phase difference of 180∘ or 120∘.