An electrical device draws 2kW power from AC mains (voltage 223V (rms) = 50,000 V). The current differs (lags) in phase by φ (tan φ = -3/4) as compared to voltage. Find (i) R, (ii) XC – XL, and (iii) IM. Another device has twice the values for R, XC and XL. How are the answers affected?
tanϕ=RX1−X2=4−3 ⇒ X1−X2=4−3 R Imnpedance z=R2+(X1−X2)2 ⇒ z=R2+R2(169) ⇒ z=45 R Now, Irms=zVrms=(45 R)223 Power =Irms2z=(5 R/4223)2×45 R=2×103 W ⇒ R=29.1 Ω ⇒ R=20 Ω (B)
