What is the approach to solving this AC circuit voltage problem using phasors?

[aryan pandey]

Homework Statement

the problem is given in the attachment

Homework Equations

basic knowledge of ac circuits and phasor diagrams

The Attempt at a Solution

for point A , i calculated the potential easily. and for point B , i calculated the potential using phasor relationship .. now after doing V_A - V_B, i got the relation that its modulus will first decrease and then eventually increase
but in the answer given is that modulus of V_A - V_B will remain unchanged.

 

[gneill]

You'll have to show the details of how you got your relation. Can't fix what we can't see

 

[aryan pandey]

truely speaking , i am confused how to proceed this question and hence not able to provide my approach .
through this question i want to grasp the concept of the question.

 

[cnh1995]

truely speaking , i am confused how to proceed this question and hence not able to provide my approach .
through this question i want to grasp the concept of the question.

Well, could you post the phasor diagram that you've drawn?
What can you say about the locus of V_B from the fact that R1 and R2 are equal?

 

[Diegor]

truely speaking , i am confused how to proceed this question and hence not able to provide my approach .
through this question i want to grasp the concept of the question.

You should think about the extreme cases. What hapen when R=0 and when R tends to infinity maybe that helps as a start. Anyway you have to get an equation for Vab in function of the variable recistance.

 

[gneill]

truely speaking , i am confused how to proceed this question and hence not able to provide my approach .
through this question i want to grasp the concept of the question.

Start by writing expressions for the potentials at points A and B. You referred to phasors, and that's a great idea. You can work graphically or algebraically (complex value phasor representation). The complex value method employs complex impedances.

Hint: Since the AC frequency is not changing the reactance of the capacitor will not change: It will be a constant. So just assign an arbitrary name to the capacitor impedance, say -jZ. (You do recall that in terms of phasors the impedance of a capacitor has a negative imaginary value, right?)