In a black box of unknown elements (L or R or any other combination), an ac voltageE=E0 sin ωt+ϕ is applied and current in the circuit was found to be I=I0 sin ωt+ϕ+π/4. Then the unknown elements in the box may be

Since current is leading emf, capacitor must be present in the circuit. Along with capacitor, there can be either (i) only resistoror (ii) resistor and inductor if XC > XLIn both of the above conditions, we can obtain a phase difference ofπ/4 with current leading emf