# Tag Info

8

1) If you are thinking of harmonics as sinusoidal waves, well yes, ALL waveforms are (can be described as) sum of harmonics. This is essentially the idea of the Fourier analysis. The problem is that to exactly reproduce a desired waveform you need in general an infinite number of harmonics. This is for instance the case of square waves. So in reality you ...

6

I've found this to be the case, too. Generally, my shop lights will flicker when turning on, especially when it is colder outside . There are two basic phases to this kind of light bulb: a start-up phase, and an operating phase. The start-up requires more voltage, because you are initiating the plasma stream between the terminals of the bulb. So, these ...

5

It is not the most straightforward viewpoint to say that a device "needs 1500 watts". This is more a consequence than a condition. What happens is that you create an electric circuit by plugging in a device into the outlet. That circuit follows Ohm's law: $$V = I R$$ So for a given voltage and resistance a certain current $I$ will flow. The power is simply ...

5

When there is no resistance, as is the case with an ideal wire, any value of current satisfies Ohm's Law: $V = I R$ since both $V=0$ and $R=0$. UPDATE: But isn't V is like what causes the current? Perhaps a mechanical analogy of the resistor will help. Consider the dashpot where the velocity of the arm is analogous to current while the force acting ...

4

EDIT: Put simply, potential difference is the work done by electrostatic force on a unit charge, while EMF is the work done by anything other than electrostatic force on a unit charge. I don't like the term "voltage". It seems to mean anything measured in volts. I'd rather say electric potential and electromotive force. And the two are fundamentally ...

4

That schematic is quite confusing; draw it with higher voltages at the top, lower voltages at the bottom, and signals flowing from left to right per standard procedure. It's also helpful to label components and nodes so that you can solve the equation symbolically. I haven't labeled some of the nodes here because they can be represented by the names of ...

4

The battery has in both cases the same energy content, so it just depends on which method uses more energy per time. This power depends on the resistance $R$ you use to connect both terminals, with a given voltage $U$ derived from Ohm's law: $$P = U^2 /R$$ So, the smaller the resistance, the faster your battery will lose it's stored energy. The copper wire ...

4

If you are wondering about causality, then I think that voltage difference $\Delta V$ is fundamental as it is the cause, and the current $I$ is the consequence. If you want to have current, you need movement of the charges. The most obvious way to move charges is to act upon them with electric field, and each electric field is accopmained with voltage ...

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

When you say "we see that if the current doubles then the potential difference is halved," you're assuming that $P$ is fixed, whereas when you say "doubling the current should increase the potential difference" you're assuming $R$ is fixed. But in fact, it isn't possible to change the current while keeping both of these things constant. Let us assume that ...

4

Assuming you mean a macroscopic potential difference, the largest I know about was in the Nuclear Structure Facility accelerator at the Daresbury laboratory in the UK, and this was 30MV. The Wikipedia article on electrostatic particle accelerators claims this is about the highest possible in such devices.

4

Let me first comment that the statement electric fields cancel while the electric potentials just add up algebraically is not actually correct. Electric fields add due to the principle of superposition (see the section on superposition in the wikipedia article). However, when two electric field vectors are of the same magnitude but point in ...

4

Perhaps I can clarify what I'm trying to get at with the famous waterwheel analogy 99 years ago, Nehemiah Hawkins published what I think is a marginally better analogy: Fig. 38. — Hydrostatic analogy of fall of potential in an electrical circuit. Explanation of above diagram In this diagram, a pump at bottom centre is pumping water from right to ...

4

Well, your lecturer certainly shouldn't have put it like this, however it's true that you have got a lot wrong here. It's stuff you definitely will need to understand better if you're studying power engineering. First, you seem to think that electrons are attracted by magnetic north poles. They aren't; in fact stationary charges and magnetic fields aren't ...

3

1) Putting an electron in a loop would measure it's spin. You have to get it to the loop and that involves a change of flux 2) Your magnetic field went from $\frac{1}{\sqrt{2}}|B_\uparrow\rangle+\frac{1}{\sqrt{2}}|B_\downarrow\rangle \to |B_\uparrow\rangle$ Now I don't know how Maxwell's laws work on wavefunctions, but it definitely didn't start at 0. In ...

3

There is no 'potential' to measure when you have varying magnetic field, as the electric field has non-zero curl then, and does not behave as gradient of any potential. So there is no electric potential kind of 'voltage'. There is only the electromotive force kind of 'voltage', which is defined on a loop. edit: To address the question for measuring integral ...

3

If it's a light bulb or heater, it's just a resistor. First, forget that it's alternating current, just to simplify things. Think of the power source as a really big 220 volt battery. If it's drawing 1500 watts, divide that by 220, and that will tell you the current I in Amperes. (That just measures how many electrons per second are flowing. An Ampere is ...

3

Yes, the electron is accelerated by the external electric field $E$, but at the same time it is "decelerated" with collisions with obstacles. These collisions are modelled as a "friction" force proportional to the electron velocity, something like this: $$m_e\frac{dv}{dt} = eE-r\cdot v$$ This equation has a quasi-stationary solution when the dragging force ...

3

First of: the energy W does not increase exponentially it increases quadratic! Second: What do you want? Energy density! So to get good high energy density you need high C because you can (as you already stated) only go to a certain amount of voltage until you get a breakdown. The problem is, C does not change easily. If you take a simple Plate - Plate ...

3

Is a square wave always a sum of harmonics or can we produce a square wave by quickly changing voltage? From a synthesis point of view, a square wave can be synthesized via the summation of an infinity of sine waves of appropriate frequency, phase and amplitude. From an analysis point of view, a square wave can be decomposed into an infinity of sine ...

3

How square can we make a square wave? Mostly it's a matter of rise time and fall time - how quickly the voltage transitions from one level to the other. Easily a few nanoseconds, and with the right parts, a fraction of a nanosecond. I was routinely making and measuring voltage pulses of half a nanosecond width - and that was back in the 1980s. When it ...

3

Naturally, we already have Lightning which goes to some 120 MV. A Van de Graaff Generator produces some $10^7$ volts provided a supply of only $10^4$ volts. It's the highest man-made voltage ever produced. Some high voltages produced through sparks in this article.

3

Well, let's just play an order of magnitude game. Relativity should start to show up at kinetic energies approaching a particle's rest mass. So, we have: \begin{align} qV &= mc^{2}\\ V &= \frac{mc^{2}}{q} \end{align} Using the values for the electron, we get about $5\times 10^{5}$ V for electrons to turn relativistic. Protons are going to ...

3

Voltage is a difference of potential energy for electric charges, and potentials are defined from forces, so that $F=-\nabla V$, where $V$ is the potential and $F$ is the force. When you have determined the potential $V$ you can now add any constant you want, or any function $f$ that doesn't depend on coordinates, because $-\nabla V=-\nabla (V+f)$, as $f$ ...

3

Linacs come in several types, but the kind you are talking about are segmented devices. The device is divided into multiple regions, each developing a strong electric field, but to avoid needed million volt potentials (as in a van de Graff accelerator) the regions have alternating fields at any given moment. Then you arrange for a bunch of charged ...

3

No, they do not all have the same voltage drop. If they were in series, however, they would. By Ohm's Law, the voltage drop is proportional to the current flowing through a resistor. (So in several series resistors with the same resistance, the drop across each one is the same, since the current across each one is the same). However, because B and C are in ...

3

Voltage is voltage. Electrostatic voltage is still just voltage. Materials that can store electrostatic charges are insulators (or are insulated by something), so the charge cannot leak away. Because of this they can build up a high voltage, with relatively few electrons (charge). A conducting material on the other hand needs a power source to keep the ...

3

Suppose we have a source of electrical energy, say a battery, that puts out 100 Volts. It is connected through wires with a total resistance of 1 ohm to a heater with a resistance of 99 ohms. The battery sees a total resistance of 100 ohms, and thus pushes 1 Ampere of current through the circuit. The battery is delivering energy at 100 Watts The Power ...

Only top voted, non community-wiki answers of a minimum length are eligible