Hot answers tagged electrical-engineering
8
I found a general, qualitative answer in David Blackstock's book Physical Acoustics, on page 46:
Impedance is often described as the ratio of a "push" variable $q_p$ (such as voltage or pressure) to a corresponding "flow" variable $q_f$ (such as current or particle velocity).
I also received a nice answer to this question on another Q&A site ...
6
I'll give the answer to this question using an unusual method that showed up in the American Mathematical Monthly's problem section perhaps in the late 1970s. This is not necessarily the easy way to solve the problem, but it works out nicely from an algebraic point of view.
The way most people solve most resistance problems is to use series and parallel ...
6
I'll take it step by step here. First I'll write the answer for the first few cases with circuit analysis. Then I'll apply a reduction to show the pattern that the problem arrives at.
N=1
$$Z = R+R=2R$$
N=2
$$Z = R+\frac{1}{\frac{1}{R}+\frac{1}{R + R}} = R \left( 1+\frac{1}{1+\frac{1}{1 + 1}} \right)=\frac{5}{3} R$$
N=3
$$Z = ...
6
For any given $n$, you can work it out via the rules for series and parallel resistors, but to get a general formula, valid for all $n$, doesn't look easy to me. The best way I know of is to get a recursive relationship giving the resistance of an $n$-step ladder in terms of an $(n-1)$-step ladder. If I'm not mistaken, the $n$-step ladder can be thought of ...
6
Yes Sam, there definitely is electric field reshaping in the wire. Strangely, it is not talked about in hardly any physics texts, but there are surface charge accumulations along the wire which maintain the electric field in the direction of the wire. (Note: it is a surface charge distribution since any extra charge on a conductor will reside on the ...
5
Corresponding wavelength is 22.11 meters long, but we want also to emit our EM waves into the environment. This means if we get a nice half-wave dipole antenna we would need it about 11 meters in length, $\lambda/2$. Which is quite large for mobile device.
Ok, lets reduce size by using quarter-wave antenna as in WiFi, based on ideas of quarter-wave ...
4
Every electric motor runs using the Lorentz force, so there is no difference in principle between the motor in the hard drive and an electric car motor. There are commercial 60 hp electric motors that run electric cars, so the answer is yes. It's power consumption is, well, 60 hp. That's 45000 watts, plus a little more for heating the engine and so on, so ...
4
What makes it a good idea to use RMS rather than peak values
The rms value, not the peak value, is the equivalent DC value that gives the same average power.
Recall that power is the product of voltage and current:
$p(t) = v(t) \cdot i(t)$
For a resistor, we have:
$p(t) = R[i(t)]^2$
To find the average power, we must take the time average of both ...
4
The $A/W$ units refer to the current (in Ampère) produced per Watt of light incident on the photodiode. This current-production happens when the diode operates in the so-called photoconductive mode. Since your question wasn't on the inner workings of a photodiode, I won't expand on this, but Wikipedia contains some more information if desired.
3
Here is how I would do it, following the method outlined by kleingordon in a comment. This method is less cool but more general than Carl Brannen's answer, because it will work even in the case where there are crossing wires and you can't rearrange it into a single sheet of resistive material.
Let the electric potential at $A$ be $V_A$ and that at $B$ be ...
3
As suggested by Manishearth, one can perform a $Y$-$\Delta$ transform from $Y$-resistances $R_1$, $R_2$ and $R_3$, to $\Delta$-conductances $G_1$, $G_2$ and $G_3$ (using a $123$ symmetric labeling convention), cf. Fig.1 below.
A x----x------x-----[3]-----x------x----x B
| | | |
[4] [2] [1] [5]
| ...
3
To (hopefully) answer both your questions simultaneously, think of the concept this way: let's say I have an electrical circuit which consists of a battery (your EMF) connected by wires to some unknown electrical setup within a black box. Nothing appears to be melting or catching on fire within sight (which would imply the likely existence of a short ...
3
Resistors are generally used to dimension electrical devices to the ranges in voltage, current, time constants, what have you, that are needed. In this specific example the resistor is used to dimension the voltage drop in case one of the inputs has low voltage (lower than $V$), so that a current flows from $V$ to the input (it can only flow in this ...
3
I'm not sure why the resistor to ground from B is there, but you are incorrect at point D, the capacitor doesn't pass the DC level as you've indicated. It's a high-pass filter with C and R, so basically you need to move the DC-level on the Vd plot to ground - but keep the two transients like you've plotted them. That is, the curve should start at ground and ...
3
Uh... I liked this question. And a quick look at the Google or Google scholar did not give me much. So is written here more what I grasp people understand about impedance. Like Noldorin was saying I take impedance as how much is impeding power to be transferred from one place to another. In a homogeneous medium power is transferred as wave unimpeded but when ...
3
Before I start, I should say, I am yet to meet a physicist who has a clue about the practical aspects of loudspeaker design. Likewise about audio engineers ;-) so the fact you are asking this, means you are well set up for making some good speakers.
John Bird has written an electronics textbook which could be very useful for you which covers all the ...
2
Mechanical impedance matching does have an application in electrical transmission lines (or any elastic cable/structure vibration) because it helps describe how much of the wave gets through a discontinuity, and how much is being reflected. Mechanical impedance is force over velocity and along the cable it is equal to tension over wave speed. The ...
2
The quotes you give do not really explain much.
With a conductor one can short the static field of the atmosphere, one does not need oscillations for that. I think it was Benjamin Franklin with reaching the clouds who discovered that first hand?
Lightening strikes when naturally induced upward leaders reach and meet the charged cloud downward leaders ...
2
Real LC circuits have some resistance,
which wastes some of the energy as
thermal radiation, and the cycling
eventually dies. I think they also
have some other non-idealities that
allow energy to escape as far field
electromagnetic radiation, correct?
What are these non-idealities? Are
they independent of the resistive
component?
...
2
The small matter of the magnetic saturation of iron really ought to be mentioned in this discussion. In practise, the best iron cannot sustain a magnetic field of more than about 1 Tesla, or 1 volt-sec/m^2. We must then ask: how much current does it take to drive a field of that magnitude? That depends of course on the magnetic permeability of the iron and ...
2
Let's imagine that we live in beautiful world of brush-less motors without friction.
Limitation must come from coil resistivity - the more power you pump into coils, the more losses you have due to their non-0 resistivity. At high RPM resistance also increases due to skin effect (reducing effective cross-section of the wire).
So if one want to have more ...
2
There are some missing data in your question.
What voltage does the batteries have, I'm going to assume 12V since it is common.
Battery capacity, you typed it as 150A but I guess it was 150Ah. Please note that a normal car battery on a car like a VW Golf has approx 60Ah so 150Ah is a quite big battery.
Output power, you state that you have 1000V (Volts) ...
2
Your approach is not correct.
Once you connect the two capacitors what happens is that the plates that are connected with a wire will have the same potential because they form a conductor. Suppose the initial charges are $Q_{1i}=Q$ and $Q_{2i}=0$. Because the potential difference across both capacitors is equal you get
$$
...
2
LED's are not like your standard circuit elements. Voltage current relation is highly nonlinear, so you don't generally speak the LED having a unique resistance.
The voltage vs current relation is almost vertical at the operating voltage, i.e. you will have a huge range of currents with voltage very close to say 3V. The resistance of the LED can be almost ...
2
There's no magic solution. Your options are (in something like an order of preference):
Prevent the 50 Hz from entering your signal in the first place by (a) making your setup less sensitive to the 50 Hz field, and (b) removing sources of the 50 Hz field.
Filter out the 50 Hz with a notch filter.
Subtract the 50 Hz signal by using a magnetometer (i.e. ...
2
Yes, such an engine would be possible. For a circular motion you would need to modify the setup a little bit but not significantly.
While Ron is absolutely right that there is no difference in principle a big engineering/economical problem is that an engine with such a design would need very large and powerful permanent magnets. NdFeB magnets in a size ...
2
With no resistance, the full voltage is applied to the fan, and you get mechanical work done, at whatever efficiency the fan itself is capable of. Never minding the fan itself, so far as the electrical aspect goes, you could say it's 100% efficient.
With resistance in the system, for example about equal to the resistance of the fan, you have less current ...
2
There are two types of energy source. 1. Voltage source 2. Current source
In voltage source, source voltage remains constant in spite of varying load resistance connected to it.
In current source, current remains constant through the load in spite of its resistance.
The main line is a voltage source.
so the power consumption (electric energy) used bye ...
2
We can store electricity directly, only in a system with a decent amount of capacitance. i.e. in capacitors. Hoever, in general, electricity grids have next-to-no capacitance; so the electricity comes straight from the generator to you.
There are lots of ways to store electricity indirectly, and on electricity grids, that's almost exclusively done by ...
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