Q4. Assertion: an ideal inductor in an ac circuit draws no net energy from the source over a cycle. Reason: its current is π/2 out of phase with the voltage, so the power iv averages to zero over a cycle. Are both true, and does the reason explain the assertion?
Both are true, and the reason explains the assertion (NCERT pages 182–183).
Q5. At what frequency does a 0.20 H inductor have a reactance of 1.0 kΩ?
ν = XL/(2πL) = 1000/(2π × 0.20) ≈ 796 Hz (NCERT Eq. (7.13), page 182).
Q6. A coil of negligible resistance draws 2.0 A rms from a 200 V, 50 Hz supply. Find its inductance and the peak current.
XL = 200/2.0 = 100 Ω, so L = 100/(2π × 50) ≈ 0.32 H; the peak current is √2 × 2.0 ≈ 2.8 A (NCERT Eqs. (7.13)–(7.14), page 182).
Q7. Why does an inductor pass a steady direct current easily but oppose a high-frequency current strongly?
XL = 2πνL is zero for dc (ν = 0) and grows in proportion to the frequency, so the inductor offers almost no opposition to dc and a large one at high frequency (NCERT page 182).