EGR 203 Electric and Electronic Circuits Assignment 14

  1. The heating element in a soldering iron has a resistance of 30 Ω. Find the average power dissipated in the soldering iron if it is connected to a voltage source of 117 V rms.

  2. A current of 4 A rms flows when a neon sign is supplied by a 110-V rms power system. The current lags the voltage by 60°. Find the power dissipated by the circuit and the power factor.

  3. A drilling machine is driven by a single-phase induction motor connected to a 110-V rms supply. Suppose that the machining operation requires 1 kW, that the tool machine ihas 90 percent efficiency, and that the supply current is 14 A rms with a power factor of 0.8. Find the AC machine efficiency.

  4. A single-phase circuit is placed across a 120-V rm, 60-Hz source, with an ammeter, a voltmeter, and a wattmeter connected. The instrucments indicate 12 A, 120 V, and 800 W, resppectively. Find (a) the power factor, (b) the phase angle, (c) the impedance, and (d) the resistance.

  5. For the following numeric values, determine the average power P, the reactive power Q, and the complex power S for the circuit below. Phasor values are rms.
    1. vs = 650 cos(377t) V
      iL = 20 cos(377t − 10°) A
    2. Vs = 460Ð0° V
      IL = 14.14 Ð−45°

  6. For the circuit above, determine the power factor for the load and state whether it is leading or lagging for the following conditions:
    1. vs = 540 cos(ωt + 15°) V
      iL = 20 cos(ωt + 47°) A
    2. vs = 155 cos(ωt − 15°) V
      iL = 20 cos(ωt − 22°) A

  7. A single-phase motor draws 220 W at a power factor of 80 percent (lagging) when connected across a 200-V, 60-Hz source. A capacitor is connected in parallel with the load to give a unity power factor, as shown below. Find the required capacitance.


Maintained by John Loomis, last updated 20 July 2012