# Tag Info

23

Suppose you are using a waterwheel to do some form of work (e.g. grind corn). You need a head of water to make the wheel move, and you could use either 1kg of water at a height of a million metres or you could use a million kg of water at a height of one metre. In both cases the water would do the same amount of work as it flowed through your wheel. The ...

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 ...

8

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 ...

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

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 ...

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 ...

5

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 ...

5

By Ohm's law, which states V = IR, where V is the voltage accross a resistor, I the current thru it, and R the resistance. The units work out so that no additional proportionality constant is required when V is in Volts, I in Amps, and R in Ohms. For example, if the 1.5 V battery is connected to a 47 Ω resistor, then 32 mA will flow. Of course you ...

5

Voltage is similar to height. It plays the same role for electric charge as height*gravity does for a ball on a hill. So high voltage means high potential energy the same way a ball being high up on a hill means high potential energy. Voltage is not potential energy, the same way height is not energy. However, if you have a certain amount of charge $q$, you ...

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

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

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

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

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 ...

4

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 ...

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

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

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

Voltage is the unit of electric potential, the electric potential difference (in your case, the potential difference between the two ends of resistor in a circuit) can be called the voltage drop. The potential difference produces an electric field $\vec{E}$, and the direction of $\vec{E}$ points from high potential to low potential. The electric field ...

3

This is Catch 22 type of question. Of course resistance of the voltmeter is never infinitive and of course some current does flow through the voltmeter. The idea is that resistivity of the voltmeter is much larger than other resistivities, i.e. $$R_V \gg R_1, R_V \gg R_2.$$ If switch SW1 is open, then current through voltmeter equals ...

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

If we model the path for the current through the human body as a resistor, then by Ohm's law, the current and voltage are proportional. That is, a greater current through the body will be associated with a greater voltage across the body. Having said that, let's consider the source of the shock. It is the case that sources may produce a large voltage but ...

3

You see, current in one direction indicates the flow of free electrons in the other direction. Hence, current flows. But voltage does not flow. It's actually the work done per unit charge. (Joule/Coulomb). In other words, it's an energy or simply the potential difference between two points. Sometimes, a bird does not get a shock while resting on a carrier ...

3

In many applications we are interested in the power. For example your electricity bill is based on the power you consume. For a DC source the power is: $$W = VI = \frac{V^2}{R}$$ and for an AC source (assuming a resistive load so the voltage and current stay in phase): $$W = V_{rms}I_{rms} = \frac{V_{rms}^2}{R}$$ So using the RMS values makes the ...

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 ...

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