Try it on paper first. A hint, the key idea and the worked solution are here when you need them.
A series circuit has , H and . It is driven at Hz and then at Hz. For each frequency, find the phase angle and say whether the current lags or leads. Count a lead as a negative angle.
In a series circuit the same current flows in every part. The reactances are and , with . The impedance is , and holds for peak or for rms values. The phase is . A positive means the current lags.
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. At Hz. . . . The net reactance is . So and . The capacitor wins, and the current leads.
Step 2. At Hz. . . . The net reactance is . So and . The coil wins, and the current lags.
Answer: at Hz, where the current leads, and at Hz, where it lags.
Watch out. Both angles are close to . The resistance is small next to the reactances, so the circuit behaves almost like a pure capacitor at Hz and like a pure coil at Hz. Between the two frequencies lies the one where .
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