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Homework Help: Inductance & Resistance in AC

  1. Oct 28, 2007 #1
    1. Inductor & Resistor connected in series
    A circuit comprising of an Inductor & Resistor connected in series.
    The values are:
    R1 resistor Value 680Ω
    Resistance of the Inductor's Windings: (R of L) 98.2Ω
    Supply Voltage: 13.2V
    Circuit Current: 8.1mA
    Supply Freq: 50Hz
    Voltage across the resistor R1 5.5V
    Voltage across the inductor 10.4V

    1. Use Ohm's Law to find the voltage dropped across the resistance of the inductor's windings (R of L)

    2. Add this value to the voltage dropped across the resistor R1

    3. Draw a scaled phasor diagram of the resistive voltage and the supply voltage, to find the voltage dropped across the pure inductance.

    My solution so far:

    1. = 8.1mA * 98.2Ω = 0.8V
    Voltage dropped across R1 = 8.1mA * 680Ω = 5.5V

    2. = 0.8V + 5.5v = 6.3V

    3. This is where I get stuck

    Can anyone Help!!!!
    Last edited: Oct 28, 2007
  2. jcsd
  3. Oct 29, 2007 #2


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    Homework Helper

    Draw a line AB of length 13.2 cm, which represents the supply voltage. From A draw an arc of length 5.5 cm, which represents voltage across R. From B draw an arc of length 10.4 cm, which represent the voltage across L.. Find the point of intersection C. Join AC. Drop a perpendicular from B to AC produced. The length of the perpendicular is the voltage across the pure inductance.
  4. Oct 30, 2007 #3
    Thanks rl bahat.

    That works fine... I couldn't see the wood for the trees!
    Once again
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