1. ### Frequency in an AC circuit given capacitance, voltage, and current

By combining the formula for the reactance of a capacitor with Ohm's Law for a capacitor, I can solve for angular frequency, and divide by 2π to find frequency. The resulting equation is: f = I/(2π VC) Using the given values, I end up with 5.2 kHz, instead of the correct answer of 5.2 MHz. I...
2. ### Current through source in AC circuit with R & LC in parallel

Homework Statement In the circuit diagram shown , Xc = 100 ohm , XL = 200 ohm , R = 100 ohm , the effective current through the source is ? Homework Equations Z= √( R^2 + ( XL - Xc)^2) Vrms = Irms/ Z The Attempt at a Solution I tried to draw the phaser diagram and calculate the relation...
3. ### If the AC EMF is 0 at t=0, then how does current pass through a capacitor?

Hi, I have a problem understanding the ac capacitive circuit, where Vc = Vm * sin(ωt), and, current leads the voltage, so at t = 0, v = 0 which means no emf, no pushing energy for the electrons, I think, then how current is max? what is the energy source that supplied the electrons with the...
4. ### Easy way to calculate losses for re-purposing a transformer?

Hi everyone! This is my first thread :) I've been working a bit with AC and radio, and would like to make a simple(-ish) circuit in which a 1-volt peak audio signal is stepped up to around 5 volts with a transformer, and is fed into a crystal oscillator to make a crude-but-effective AM...
5. ### Computation of Thevenin Equivalent

Hello! Recently I was going through some old exams and upon encountering this problem (which seemed pretty easy) I got stuck. Exams at my university are composed of individual tasks, each having three subquestions with four plausible answers respectively. Solution sheet gives results only, so...
6. ### AC circuit voltage homework

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...
7. ### Complex Power

Homework Statement y = 27 Homework Equations The Attempt at a Solution - I calculated the total impedance. - Divide it with the voltage to get the current. - Then I use the load impedance to find the voltage load. - And I calculated the complex power for the load. I am not comfortable...
8. ### Width of Resonance in RLC-circuit

Homework Statement In an undriven RLC-circuit, the characteristic time of the capacitor, ie the time taken for the amplitude of the capacitor voltage ## V_c ## to drop by a factor e, is ## T = 2L/R ##. We now have a RLC-circuit which is driven by a AC voltage of variable frequency ## \omega ##...
9. ### RLC Black box at different frequencies

Supposed there is a black box connect to an AC circuit. Inside the black box, there are either a resistor connected with a capacitor or a resistor connected with a inductor. They can be connected either in series or in parallel. The total impedance and phase shift of the black box at 2 different...
10. ### Engineering AC circuit with a switch -- analysis

Homework Statement Given the circuit of sinusoidal current (attachment1) with given data: \underline{Z_3}=200(3-j4)\Omega,\underline{Z_4}=100(3+j20)\Omega,\underline{Z_5}=100(3+j4)\Omega,\underline{Z}=100(2+j5)\Omega,\underline{I_{g2}}=-10(2-j)mA. After the switch is closed, the increment of...
11. ### Engineering Circuit analysis -- Find the complex apparent power of I(g2)

Homework Statement Given the circuit of sinusoidal current (attachment 1) with given data: \underline{Z_3}=200(3-j4)\Omega, \underline{Z_4}=100(3+j20)\Omega, \underline{Z_5}=100(3+j4)\Omega, \underline{Z}=100(2+j5)\Omega, \underline{I_{g2}}=-10(2-j)mA After the switch is closed, the increment...
12. ### Engineering Circuit analysis -- Find active and reactive power in the branch...

Homework Statement Given the circuit of sinusoidal current (attachment 1) with given data: \underline{E}=100V,\underline{E_1}=40V,\underline{Z}=(10+j10)\Omega,\omega=10^5rad/s,L=1mH, C=0.1uF. Find \underline{I_L},\underline{U_{16}}, active and reactive power in the branch 2-5. 2. The...
13. ### Excess Energy Saving from a constant energy source.

Hello everyone. So i live in Lebanon, and since a long time now we have constant power cuts, almost half the day each day. For that the Lebanese made up a system in which each neighborhood has power generators providing electricity to the residents when the power is out. Usually the owners of...
14. ### What exactly does the capacitor do in a Tesla coil?

In all tutorials I have read on tesla coils, they have said to use a capacitor spark-gap configuration, to create a tank circuit. I want to know exactly what this means, and what is its purpose. I am not going to build a Tesla coil, I am nearly just interested in the science of it.
15. ### Can you use a tank circuit to produce an AC circuit?

Since the resonant frequency of a tank circuit, is completely adjustable, and controlled by the value inductor and capacitor you use, I was wondering if it had any other uses, other than increasing its impedance at its resonant frequency. Can if be used to produce ac signals of its resonant...
16. ### Engineering Current phase angle difference (AC circuit)

Homework Statement Three receivers, with complex impedance \underline{Z_1}=(125+j375)\Omega,\underline{Z_2}=(700+j100)\Omega,\underline{Z_3}=(500-j500)\Omega, and two sinusoidal current generators of effective values I_{g2}=40mA and unknown I_{g1} are connected. When the switch is open...
17. ### Phasor algebra in AC circuit analysis

Homework Statement Find the peak value of current through the AC source of the following L-C-R circuit, if peak voltage is ##V_0## and angular frequency is ##\omega_0##. Homework Equations I have learnt Vector algebra and calculus (single variable). I was taught how to use phasor diagrams for...
18. ### How does surface capacitive touchscreen work in detail?

It's pretty easy to find the "working principle" of surface capacitive touchscreen like http://www.elotouch.com/Technologies/SurfaceCapacitive/howitworks.asp [Broken] Roughly speaking, I know that A surface capacitive touchscreen has a conductive layer to which some electrodes are attached...
19. ### Engineering Instantaneous Current in single phase circuit

Homework Statement SOURCE: v(t) = (311)cos(314t) [v] IN SERIES WITH: R = (0.3) [Ω] L = j(0.7) [Ω] "load" = 2.5 + j(1.0) [Ω] Homework Equations Find the instantaneous current, and the phasor current. The Attempt at a Solution (1.) I first found the frequency of the source: (314) / (2*pi) ≈...
20. ### AC direction change - how does electricity flow?

If drift velocity of electrons changes in AC, how does electricity flow through a circuit to then lose potential energy to the devices in the circuit? Also considering the change in direction, does that mean that the live wire and neutral wire also switch roles in AC mains? I am very confused...
21. ### Calculating half power frequency/cutoff frequency

Homework Statement *(Problems attached as images)* For first problem: ##\cfrac{|V_2|}{|V_1|} = \cfrac{1}{\sqrt{4+(\omega RC)^2}}## For second problem: ##\cfrac{|V_2|}{|V_1|} = \cfrac{\sqrt{1+(\omega RC)^2}}{\sqrt{4 + (\omega RC)^2}}## I have to calculate half power frequency for both...
22. ### E&M: AC Circuit Light Bulb

Homework Statement How large an inductance should be connected in series with a 120 volt (rms), 60 watt light bulb if it is to operate normally when the combination is connected across a 240 volt, 60 Hz line? (First determine the inductive reactance required. You may neglect the resistance of...
23. ### Need help proving an equation for power loss in a dielectric

Homework Statement 2. Homework Equations [/B] I am trying to prove the equation $$\frac{\bar{P}}{V}=\frac{1}{2}E_0^2\sigma_{AC}$$ which can be rewritten as  \begin{align} \frac{\bar{P}}{V} &= \frac{1}{2}E_0^2\sigma_{AC}\\ &=\frac{1}{2}E_0^2\ \omega\ \epsilon_0\ \epsilon^{''}_r\\...
24. ### AC power source for lab

Hi. I'm joining this forum to ask about some equipment I need. At the community college where I teach, we do a lab in freshman physics where students measure the input to and output from a transformer. My AC sources are reaching the end of their lives, so I'm looking for replacements. As far...
25. ### Engineering Finding the voltage in this AC circuit

Homework Statement Homework Equations KVL at that loop The Attempt at a Solution I can easily solve all the individual current and voltages in this circuit using Mesh analysis and Gaussian Elimination. But how do I get Vx? I can simply add the voltages of the two 10uF capacitors if they are...
26. ### Phase Difference between Voltage and Current

Homework Statement The circuit above has a 29 resistor and a 11.1 mH inductor. Calculate the theoretical phase difference between the current CPA and voltage VPB if the circuit is driven by a sinusoidal voltage source with a peak amplitude of 3.5 V at the following frequencies: 20 Hz 420 Hz...
27. ### Circuit to change dc to ac?

I have only just found out about inductors, and am trying to figure out how a circuit with an inductor and a capacitor could change dc current to ac current. With the set up of the circuit, would it suffice just to have the dc supply with a 'gate' that stops/allows through the dc current with a...
28. ### Engineering AC circuit analysis -- mesh and nodal

Homework Statement Determine, using the values given in TABLE A, the current I in the circuit of FIGURE 2 by: (a) mesh analysis (b) nodal analysis. Any help verify for part (a)? And to help me get started with (b) as V3 is driving me nuts. Homework Equations The Attempt at a Solution For...
29. ### Obtain Expression For Voltage Across Capacitor

Homework Statement A voltage source given by ##v_s(t)=25cos(2\pi\times10^3t-30^\circ)## is connected to a series RC load. If R = 1MOhm and C = 200pF, obtain an expression for ##v_c(t)##, the voltage across the capacitor. Answer known to be: ##v_c(t)=15.57cos(2\pi\times10^3t-81.5^\circ)##...
30. ### Help with AC Circuit containing a motor

Hello, this is not a homework question, but is a past year exam question which I'm stumped at. Any help will be appreciated. 1. Homework Statement We're designing a current reduction system for an AC motor which is modeled as an inductor ##L##in series with a resistor ##R##. This motor is...