Calculating the effective value and frequency of AC Circuit

In summary, the problem is a circuit with AC components, where the direction of current and voltage is not specified. The ammeter and voltmeter show ideal measurements of 600mA and 60V respectively. The circuit consists of a capacitor, inductor, and resistor with values of 60nF, 100uH, and 50Ω respectively. The task is to calculate the angular frequency, effective value of the EMF, and ammeter result when the switch is open. After attempting to solve the problem using only effective values of currents, it was realized that complex analysis was needed to find the correct answers.
  • #1
diredragon
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15

Homework Statement


For AC Circuit shown in the picture, ##C=60nF##, ##L=100uH##, ##X_3=-100Ω##, ##Z_2=50Ω## and ##Φ_2=\frac {\pi}{6}##. When the switch is closed the ammeter shows a current ##I_1=0.6A## and the voltmeter shows ##U_l=60V##. The measuring instruments mentioned are ideal. Calculate:
a) ##w##
b) effective value of ##E##
c) ammeter result ##I'_1## when the switch is open.
The Circuit:
circuit.png


Homework Equations


3. The Attempt at a Solution [/B]
The first thing i noticed is that the direction of current and voltage isn't given so I need to guess it. I started from the ammeter and guessed that the flow of current is downwards.
From there, ##U_1 = I_1*X1## = -60V## with a + sign at the top node. Once i have this voltage i can find the current ##I_2 = \frac {U_1}{Z_2} = -1.2A##. With the two currents meeting at the top node, the current ##I_l = I_c## of the top node equals ##I_l=0.6A##.
circuit.png

Since i have ##U_l = I_l*wL##, ##w = \frac{U_L}{I_lL} = 10^6## which is not the correct answer.
The answer should be ##w = \frac {\sqrt 3}{3}10^6##. I can't go on solving the other parts if the first is not correct. What did i do wrong?
 

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  • #2
There are no DC voltages or amperage's in this circuit. Everything is AC.
The 60V and 600mA are presumably rms.

Also, I do not know what your "X3=−100Ω" refers to.
Unless that is the value for X1 (using a capacitor symbol).

If X1 is not a cap, then part of the circuit have a DC component to the current, but still not the volt meter.
 
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Likes diredragon
  • #3
.Scott said:
There are no DC voltages or amperage's in this circuit. Everything is AC.
The 60V and 600mA are presumably rms.

Also, I do not know what your "X3=−100Ω" refers to.
Unless that is the value for X1 (using a capacitor symbol).

If X1 is not a cap, then part of the circuit have a DC component to the current, but still not the volt meter.
The ##X_3## was supposed to be ##X_1##. I solved it now, i thought i could work with effective values of currents only but i guess i needed a complex analysis to solve it.
 

1. What is the effective value of an AC circuit?

The effective value of an AC circuit is the root mean square (RMS) value, which represents the equivalent DC value of the AC wave. It takes into account the varying amplitude of the wave and is used to calculate power and determine the behavior of circuit components.

2. How is the effective value calculated for an AC circuit?

The effective value can be calculated using the formula Vrms = Vp/√2, where Vp is the peak voltage of the AC wave. This formula assumes a sinusoidal wave shape; for other wave shapes, different formulas may need to be used.

3. What is the frequency of an AC circuit?

The frequency of an AC circuit is the number of complete cycles of the alternating current in one second. It is measured in Hertz (Hz) and is typically 60 Hz in the United States and 50 Hz in many other countries.

4. How is the frequency of an AC circuit determined?

The frequency of an AC circuit can be determined by measuring the time for one complete cycle of the AC wave and then using the formula f = 1/T, where T is the time in seconds. Alternatively, it can be measured using specialized equipment such as an oscilloscope.

5. What is the significance of calculating the effective value and frequency of an AC circuit?

Calculating the effective value and frequency of an AC circuit is important for understanding the behavior and performance of electrical systems. It allows us to accurately determine power and energy consumption, select appropriate components for a circuit, and troubleshoot any issues that may arise. It is also essential for designing and maintaining efficient and safe electrical systems.

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