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AC circuits

  • Thread starter Clari
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Hi there! I have some problems in this topic...real difficult to me. ^-^

A 1(miu)F capacitor is connected in series with a coil of R=50(ohm) and L=49mH and an a.c. ammeter. A current of r.m.s. value 0.03A and f=500Hz is passes through the combination. What is the peak p.d. across the combination?

That question is in part c, that means i have solved the peak p.d. across the capacitor(which is=13.5V) and that across the coil(which is=6.8V). well, i know the answer should not be (13.5V+6.8V), but then i dont know how... :frown:

please help me.
 

OlderDan

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Clari said:
Hi there! I have some problems in this topic...real difficult to me. ^-^

A 1(miu)F capacitor is connected in series with a coil of R=50(ohm) and L=49mH and an a.c. ammeter. A current of r.m.s. value 0.03A and f=500Hz is passes through the combination. What is the peak p.d. across the combination?

That question is in part c, that means i have solved the peak p.d. across the capacitor(which is=13.5V) and that across the coil(which is=6.8V). well, i know the answer should not be (13.5V+6.8V), but then i dont know how... :frown:

please help me.
The approach will depend on what methods you have learned. I'm guessing that you have learned about phasors, which treat the potential differences accross elements as rotating vectors with some angle between them. That angle represents the phase difference between the potentials for the different elements. The p.d. for the resistor will be in phase with the current. The p.d. for the coil will lead the current by 90 degrees and the p.d. for the capacitor will lag the current by 90 degrees. Have you heard of ELI the ICE man?

Another approach is to find the equivalent impedence of the circuit, for which you should have a formula involving a square root of some combination of circuit element parameters and the frequency. The product of the equivalent impedence times the current will give the p.d. of the combination.
 

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