Suppose you take a 2*10^2 resistor and a 0.40 inductor and make a series circuit with a voltage source that has voltage amplitude 30 and an angular frequency of 2.5×10^2 .

**Part F (The part that I need help on):

Construct the phasor diagram.

Draw the voltage and phasors with their tails at the origin of the coordinate system. The length of the voltage phasors is given in volts; the current phasor is not drawn to scale. The orientation and length of your phasors will be graded.

enter image description here

Previously found in other parts:

Impedence (Z) = 224 ?

Current (I) = 0.134 A

Voltage across the resistor (VR) = 27 V

Voltage across the inductor (VL) = 13 V

Phase angle with respect to the current (?) = 27 degrees

The source voltage leads the current

**Also, I don't know if this is fully important but the length of the source voltage vector (V) in the diagram is 30 (no units) and its angle is 48 degrees wrt x-axis. The vector for the current (I) is at angle of 21 degrees wrt x-axis and its length is not given.

I need the length and the angle of both VL and VR

  • \$\begingroup\$ Would Electrical Engineering be a better home for this question? \$\endgroup\$
    – Qmechanic
    Apr 6, 2014 at 23:22
  • \$\begingroup\$ Please show us what you have done to try to solve this yourself. Also, please fix the values like "2.0x102" and add units to resistance and inductance values. \$\endgroup\$
    – Joe Hass
    Apr 6, 2014 at 23:32
  • \$\begingroup\$ Units of ohms and units of henries are needed. Without units this is unsolvable. Also why have you specified resistance as 2.0 x 102.what on earth does that mean? 204 ohms? \$\endgroup\$
    – Andy aka
    Apr 6, 2014 at 23:35

1 Answer 1


I don´t understand some parts of your question, however I will try to answer it the best possible.

I consider that the angle of the voltage and current phasors in the shown diagram are given.

First thing to start with a diagram always is to set up your Kirchhoff laws, in this case the one for meshes:

$$ \underline{V} = \underline{V}_R + \underline{V}_L = R~\underline{I} + j \omega L ~ \underline{I} $$

Since the current through resistor and reactor is the same, you can see that the both partial voltages have to be orthogonal to each other. Also, you know that current and voltage in an resistor are in phase while voltage leads 90 degrees in a reactor. Now you should be able to construct the diagram. If the resistor voltage phasor is parallel to the current phasor and the sum of resistor and reactor end up at the same point as the source voltage, chances are high you did it right.


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