| AC Voltage and Current Interview Questions |
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Unbalanced Three-Phase Loads
Three-phase loads are common in AC systems. When the system is balanced, the analysis can be simplified to a single equivalent circuit model. However, when it is unbalanced the only practical solution involves the solution of simultaneous linear equations. Download the file http://numericalmethods.eng.usf.edu/mcd/... from the Holistic Numerical Methods website for more background on this problem. Solve the example problem given Figure 4 in the document for the six currents. Use these values to calculate the voltages across the three motor terminals, VAN, VBN, and VCN. For more information, see http://numericalmethods.eng.usf.edu/mcd/...
Extra Credit: Solve this problem using a C++ complex number class.
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the diagram below describes a parallel AC circuit containing a resistor, a capacitor, and an inductor. The voltage across each of these elements of the circuit is the same; on the diagram, it is represented by the vector labeled V_0.
http://i20.photobucket.com/albums/b241/t...
The currents in the resistor, the capacitor, and the inductor are represented respectively by which vectors?
A) I_1; I_2; I_3
B) I_1; I_3; I_4
C) I_1; I_4; I_2
D) I_1; I_2; I_4
E) I_1; I_3; I_2
Any help is appreciated Thank you
Sincerely,
PhysicsDisciple
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I often find myself digging through multiple drawers full of DC adapters to find one the right size voltage and for another progect picked up a VariAC and a bridge diode to power a 1HP DC motor. This was the first time I have ever used one like that and got me thinking, can I just throw a resister of the right size on the input AC side and get the 3, 6, 9, 12... volts I am always looking for? For example, I am using a 6V car battery charger to power my infant daughter's swing so I don't need to buy batteries but would love to have something so much smaller and easier to leave in place.
I am assuming the equation I need is V=IR but what is my current? I mean on something so small as a baby swing I couldn't be sure. Any help would be appreciated.
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A series AC circuit contains a 67 ohm resistor, a 320 mH inductor, a 2.6e-6 F capacitor, and a generator with maximum voltage of 230 V operating at 50Hz. Calculate the inductive reactance. Answer in units of ohms. Calculate the capacitive resistance. Answer in units of kilo ohms. Calculate the maximum current in mA, the impedence in kilo ohms and the phase angle answered in between -180 and 180 degrees.
I am stuck on this section of my homework and any help would be great!!
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Ok so I'm looking on the back of two units. One unit says:
120v AC at 60Hz and at 27w (v = volts and w = watts and Hz = Hertz)
another unit says:
12v DC at 39w.
Now I'm trying to convert these both to amps using the formula:
Amps = Watts / Voltage .
For the first one, I got 0.225
For the second one I got 3.25
I'm assuming that the huge difference in numbers is because one is DC current and yes does require a power converter to run. With that said though, what's the average amount of power needed to power both devices? (like what's the minimum that a source needs to be to power both devices)
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Available information are the length of the cable, the cross section diameter of the cable, the voltage and the amperes. For example, what is the voltage drop across 100 feet of 6mm diameter copper cable from a 12 volt AC source at one end and having a 300 watt light at the other end? The current in the cable is 25 amps.
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I am trying to make a high voltage power supply, with the coil as its main supply, although I can't even get a spark out of it, I am using a 12v dc 1.5 amp power supply and am connecting one lead while I brush the other lead on, I get nothing more than a light crackle coming from the contact, not the HV output. It should be working condisdering every time I brush the contact on, it is acting as a pulsating dc supply, I was told the amperage is not enough, but I would think that it would be too much considering the output current should be lower shouldnt it, I mean a coil like this usualyl works on high frequency ac. Can anybody help me out with getting this thing to work, some of you have already given me some good advice, but I still need more after having tried many things. Is my power supply too weak,what happening, thanks.
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Well, I was measuring voltage in one of my wall outlets and I had the meter in DC mode instead of AC and all of a sudden there was this really loud pop that came from the meter and the whole back side looks kinda burnt. The meter wasnt too fancy, just one of those generic 15 dollar ones. I guess im looking for a technical explanation of why the meter blew up. I've made the same mistake with a much more expensive meter but nothing happened to it. I'm guessing too much current or something? I realize its not suppose to draw current in Volts mode so im not sure.
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11. To measure an unknown line voltage at an electrical outlet,
A. set the function/range switch to 1000 volts DC/V and insert the test leads in the
outlet. Observe the polarity.
B. set the function/range switch to the highest ohm range and insert the test leads in
the outlet.
C. set the function/range switch to 10A-DC and place the red test lead in the 10 amp
jack. Insert the test leads in the outlet.
D. set the function/range switch to 750 volts ACV and insert the test leads in the
outlet.12. Assume that the function/range switch is on the 20 kO position and the multimeter displays
“1” when the test leads are across an unknown resistor. What would most likely
cause the meter to display “1” ?
A. A weak battery
B. The function/range switch not set on a high enough scale
C. A faulty ON/OFF switch
D. Shorted test leads13. When measuring current, always place the meter in
A. series with the circuit. C. the highest DC volts position.
B. the highest AC volts position. D. parallel with the circuit.14. Assume a device draws 50 mA of current and 150 VDC across it. What is its resistance?
A. .3 kO C. 7.5 kO
B. 3000 O D. 7.5 O15. What precaution should be observed when the multimeter isn’t being used?
A. The selector switch should be placed in the ohms postion.
B. The test leads should be shorted together.
C. The selector switch should be in the hFE postion.
D. The selector switch should be in the OFF position.
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In a DC system, if u are given the potential at two points to be equal, say 220 V, u can well be sure that no current can flow between them ie., we wont experience a shock if we touch these points each in one hand (of course, without being grounded).
But is this true for AC?
Given two points are each at 220 V, it is clearly the rms value. One voltage wave may be at its positive peak and the other at the negative one. So, wont the current become [220- (-220)] / R ?
(R is the resistance of our body).
Under the above context, isn't the concept of RMS value misleading the physical reality??
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Hello,
I suspect my charger is ruining a lithium battery of mine.
I'm not happy with the performance of my battery at all.
Charger is a Hyperion 0606i and battery is a Mystery 7.4 900mAh battery.
One thing to note is that while charging, the charge current is never constant; it would bounce from 1A and .5A every second. Charge voltage is relatively stable.
Is my charger stuffed?
I'm using a 12v. 1A unregulated AC to DC wall adapter.
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1: What is a common way to create direct current electricity?
A) Atomic energy
B) Use a battery
C) Lightning
2: What happens when a light burns out in a series circuit?
A) The other lights remain lit
B) The voltage increases dramatically
C) The circuit is broken
3: What is the frequency of AC in the United States?
A) 60 Hertz
B) 50 Hertz
C) 60 cycles per minute
4: Suppose you have a wire connected to a piece of iron making an electromagnet. If you cut the voltage in half but double the number of turns of wire, what happens to the strength of the electromagnet?
A) It switches direction
B) It is 2 1/2 times stronger than it was before
C) It stays approximately the same
5: If you wanted to place three lights in a circuit, with each being an equal brightness, what kind of circuit would you use?
A) series
B) parallel
C) electromagnetic
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: What is a common way to create direct current electricity?
Atomic energy
Use a battery
Lightning
2: What happens when a light burns out in a series circuit?
The other lights remain lit
The voltage increases dramatically
The circuit is broken
3: What is the frequency of AC in the United States?
60 Hertz
50 Hertz
60 cycles per minute
4: Suppose you have a wire connected to a piece of iron making an electromagnet. If you cut the voltage in half but double the number of turns of wire, what happens to the strength of the electromagnet?
It switches direction
It is 2 1/2 times stronger than it was before
It stays approximately the same
5: If you wanted to place three lights in a circuit, with each being an equal brightness, what kind of circuit would you use?
series
parallel
electromagnetic
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A 50ohm resistor in parallel with another 50ohm resistor would read how many ohms?
25 ohms
50 ohms
100 ohms
250 ohms
When attempting to find intermittent problems in a circuit, which of the following could be attempted?
Heat various parts of the circuit
Cool various parts of the circuit
Change the supply voltage
Vibrate various parts of the circuit
All of the above
What piece of equipment is used to protect the technician from a potential fatal shock when working on hot chassis products?
Circulation transformer
Isolation transformer
Steppe transformer
None of the above
A transformer which is said to increase current from primary to secondary is called a _______
Circulation transformer
Isolation transformer
Steppe transformer
None of the above
A 2SD transistor is said to be what type of transistor?
NPP
NPS
NPN
Open circuit
None of the above
How would you best confirm an electrolytic capacitor is good?
Ohm meter
ESR meter
LCR meter
Multi-meter
The unit you are about to work on has an "AC" fuse blown. Please select the answer below that best fits your troubleshooting approach.
Replace the fuse and turn unit on
Check the "AC" supply for shorts and replace components as necessary
Check the customer's outlet for proper "AC" output, if okay replace fuse and turn unit on
Reset fuse button, evaluate operations and check for current
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