How does the sign of the phase angle φ, by which the supply voltage leads the current in an LCR series circuit, change as the supply frequency is gradually increased from very low to very high values.
The phase angle ′ϕ′ by which voltage leads the current in LCR series circuit where XL>XC. tanϕ=RXL−XC=R2πvL−2πvC1 If v is small XC>XL so [2πvL−2πvC1] is negative, so tanϕ<0. For v is large, XL>XC So XL=XC is positive or tanϕ>0 For XL=XC i.e. at resonant frequency XL−XC=0 so tanϕ=0. So phase angle in series LCR ac circuit will change from a negative to zero and then zero to positive value.
