1. Jul 2, 2011 #1

   joema

   

   The question is: "In polar coordinates, what is the impedance of a circuit that has an admittance of 7.09 millisiemens at 45 degrees?"
   
   The official answer is: "141 ohms at an angle of -45 degrees".
   
   I don't understand this. 7.09 millisiemens is 141 ohms, and the positive phase angle indicates inductance, IOW a positive y value.
   
   It seems the correct answer should be 141 ohms at an angle of 45 degrees, not -45 degrees.
   
   Please help me understand this.

    

   joema, Jul 2, 2011
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3. Jul 2, 2011 #2

   tiny-tim

   

   Science Advisor

   Homework Helper

   hi joema!
   
   admittance and https://www.physicsforums.com/library.php?do=view_item&itemid=303" are both complex numbers
   
   admittance is defined as the inverse of impedance
   
   

   the inverse of Re^iφ is (1/R)e^-iφ ​

   
   (so the phase of admittance is always minus the phase of impedance)

    

   Last edited by a moderator: Apr 26, 2017

   tiny-tim, Jul 2, 2011

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