# AC in RLC circuit questions

#### xenotime

Joined Nov 10, 2007
5
Hi all. Just started studying electronics part-time and I'm stuck with few questions.

1. A coil of 1.25H inductance and a resistance of 600 ohms is placed in series with a 4.4Kohms resistor. This circuit is now connected to a power supply of 250v at 200Hz. What is the current flowing in the circuit?

so, I know that for RL circuit the equation is I=V/Z where Z=sq root(R^2 + w^2 L^2), but that does not include coil resistance (600 ohm here). How do I solve that?

2. A circuit consists of a 300 ohm resistor in series with a 3H coil and a 5uF capacitor. Determine the tangent of the angle of phase difference between the current and the applied e.m.f when the frequency is: a) 50Hz, b) 25Hz.

as far as I understand it is : tan()= (Xl-Xc)/R. is that correct?

3. Calculate the resonant frequency of a circuit consisting of a 400 ohm resistor in series with a 0 8.H coil and a 3uF capacitor.

now, I know how it goes for LC but not for RLC.

4. A circuit consists of a 0.16uF capacitor connected across a 20v, 1kHz supply. Also in parallel with the capacitor there is a 1K ohm resistor in series with a 0.16H coil. Calculate:
a) the current drawn from the supply; b) the phase angle of this current.

It doesn't sound that bad but i need to use j-operator in this one. And was never any good with complex notations.

Any help appreciated. Thx.

#### techroomt

Joined May 19, 2004
198
1. if you apply the inductive reactance formula (Xl = 2 pi F L) for the given value (wire resistance not appled) and place it in series with the resistor value the current can be calculated.

2. Xc and Xl must both be calculated resulting in phasors 180 deg apart. apply the forula you gave.

3. in a resonant circuit Xl = Xc. sub in the other equations you know for these.

4. more of the same but in parallel.