# Tag Info

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The electric field assigns a single vector quantity to each point in space (specifically, the direction in which a positive test charge would accelerate if it popped into existence at that point, assuming it didn't perturb the setup creating the field in the first place). I believe that the difficulty of this question arises from an ambiguity in the problem ...

5

In the left image, the vehicle is prevented from moving downwards as the ground is exerting a force upwards equal to the force of gravity on the vehicle. However, in the case of the electric circuit, there is no such opposing force. The orientations of the conductors attached to the battery terminals doesn't have an effect on the flow of electrons (unless ...

4

Faraday's cage is known to block static and non-static electric fields. The mechanism of blocking depends on whether the electric field is static or non-static (EM field). I suppose you question is about how the cage works in non-electrostatic case. In EM case (time changing field), two scenarios could happen. The first is electric discharge where the ...

3

The mistake comes from averaging V and then squaring the average. If you squared the voltages and then found the weighted average of the squares, the result would match your initial calculation. There is another, more basic way to calculate the average power. Find the energy released during each of the two periods; add the two amounts of energy and ...

3

Yes, and in fact there are several types of electrical chargers that you power by walking. Typically you'd use these for low power applications such as recharging your mobile phone as you walk. There are a lot of frankly daft designs out there, but this one is being funded by the US military, which may or may not be daft depending on your views of the ...

3

I think you're confusing "electric potential" and "electric potential energy". I don't blame you, it's an unfortunate bit of terminology. The electric potential energy is defined for a particular charge (or distribution of charges), and so you need to explicitly put in the charge of the point or distribution of interest. That is, we don't talk about the ...

3

The electrostatic potential energy of a system of point charges is defined as the work required to be done to bring the charges constituting the system to their respective locations from infinity. Suppose we have a configuration of point charges. If the potential of the energy of the system is negative, this means work is positive. Consider two point ...

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These scams typically operate in a very formulaic manner: first they make large press releases for the concept, ask for funding, find funding, make press releases claiming they are a year away from releasing a gigantic version of it, cite technical difficulties when the release date passes and ask for more funding, and so on. They never ask for funding to ...

3

You can reconcile both trains of thought by reconsidering your thoughts about pushing:- For DC circuits without changing magnetic fields, the voltage is the energy gained or lost per unit charge in moving from one position to another, say from the positive to the negative terminal of the battery. What a battery does, is that it creates certain ...

3

You are right in that a magnetic field is build up, which generates a electric field opposing the given potential. But the consequence is not an oscillation of current, but only a damping of the increase of the current. Therefore, if you have a Heaviside step function for the voltage, it'll result in an "exponential" increase of your current ($I(t) = I_0 ... 2 Rule of thumb for working it out: If you imagine letting a charge go, the direction it tends to move is toward lower potential energy. The opposite direction is toward higher potential energy. This is independent of the choice of where the zero of energy is. 2 This article is very good in describing the dangers of electricity, which I suggest you read. http://www.allaboutcircuits.com/vol_1/chpt_3/4.html To summarise the article,$20\text{ mA}$for$60\text{ Hz}$causes "severe pain, difficulty breathing, loss of voluntary muscle control", whereas$20\text{ mA}$for$10\text{ kHz}$is in between "threshold of ... 2 If you just plug in your suggested solution, you get $$\frac d{dt} A\cos(\omega t + \phi)+\frac 1{\tau}A\cos(\omega t + \phi)=\frac{V_{in}}\tau\sin(\omega t)\\ -A\omega \sin(\omega t + \phi)+\frac 1{\tau}A\cos(\omega t + \phi)=\frac{V_{in}}\tau\sin(\omega t)$$ Now you should be able to use the function sum formulas to solve for$\phi$and$\frac A{V_{in}} ...

2

This sound is most likely caused by the choke coil which is inside the lamps housing. It is needed for lamp starting and operation. Starting works like this: After initially the starter circuit allows for current flow through the heaters in the tube, it interrupts the the current after an initial period. This causes a high voltage impulse to be created by ...

2

A general strategy for these questions is to start at the battery and trace the current through the circuit. So, starting from the batter, we can see that the entire current passes through $R_1$. After that, the current hits a split (at the top of the circuit in your drawing), where part of it goes to the left through $R_2$ and the other part of it goes to ...

2

All materials emit thermal radiation (such as light). The hotter the material, the more the radiation is shifted to high frequencies (shorter wavelengths). The radiation comes from oscillating electrons (regardless of whether there is an electric current). Welding reaches temperatures high enough to cause significant emission of UV light. Oxyacetylene and ...

2

$\def\vE{{\vec{E}}}$ $\def\vS{{\vec{S}}}$ $\def\vA{{\vec{A}}}$ $\def\rot{\operatorname{rot}}$ $\def\grad{\operatorname{grad}}$ $\def\div{\operatorname{div}}$ $\def\ph{{\varphi}}$ $\def\vn{{\vec{n}}}$ $\def\vr{{\vec{r}}}$ The charge floating through the wire causes a current density $\vec{S}$ in the wire (not only on the surface). This causes an electrical ...

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Yes, alternating current will radiate electromagnetic waves. For example, in telecommunication, the transmitter itself generates a radio frequency alternating current, which is applied to the antenna. When excited by this alternating current, the antenna radiates radio waves.

2

No, not necessarily. Current is the just the movement of electrons already in the wire (that is neutral). The electric field (or voltage) applied causes them to have a net movement in one particular direction (i.e. opposite direction of conventional current). So copper has 29 protons and 29 electrons per atom. A copper wire would have a net zero charge. It ...

2

Jerk_dadt is correct. Electric current is the flow of free electrons in the conductor. At any instant, the number of electrons leaving the wire is always equal to the number of electrons flowing from the battery into it. Hence, the net charge on the wire is zero. If you say the current carrying conductor is charged, it will violate the Kirchoff junction ...

1

All are correct. Note that that $I$ is current passing through the resistor and $V$ is potential difference across resistor. Use those equations in which you know the values of variables and not have to calculate them. Why not use all equations in a question and satisfy yourself that all are correct? These are just using ohm's law in $P=VI$. You must ...

1

The first equation is the definition of power which is, in words, the rate of energy conversion: $$P \equiv \frac{dE}{dt}$$ Where it is understood that $E$ is the amount of energy converted. For example, in a mechanical system where gravitational potential energy is converted to mechanical kinetic energy and vica versa. In electrical circuits, the power ...

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Picking up on jinawee's answer, current is charge per unit time: $$I = \frac{Q}{t}$$ So substituting for $I$ in your second equation gives: $$P = V \frac{Q}{t}$$ But $VQ$ is just the work done, i.e. the energy, in moving a charge $Q$ through a voltage difference of $V$. So substituting $E$ for $VQ$ gives us: $$P = \frac{E}{t}$$ which shows that ...

1

Power is defined as: $$P(t)=\frac{dE(t)}{dt}$$ This is valid for any system. If energy is constant, then: $$P(t)=\frac{E(t)}{t}$$ If you're dealing with a resistance in a circuit, the dissipated power is given by Joule's law: $$P=VI$$ So the last one is a particular case of the first one.

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Three guesses: Light is composed of zillions of photons, elementary particles which even though have zero mass carry momentum. p is the momentum , h is Planck's constant, c the velocity of light, nu is the frequency In the link you gave one sees that the ping sound comes at a delta function in time of a lot of light. My first guess is that the ...

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The potential energy of a particle with charge $q$ in a conservative electric field $\vec E$ is $$U = q\phi$$ where the electric potential $\phi$ is related the electric field by $$\vec E = -\nabla \phi$$ Thus, the electric potential is defined, up to a non-physical constant, by the associated electric field - no test charge enters the picture. The ...

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Initially when you attach the capacitor to the battery, said battery will act to create an electric field within the wire. On the side of the negative terminal this field will point perpendicular to the cross section of the wire toward the terminal of the battery (electric field points toward negative charge). On the side of the positive terminal the field ...

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$20V$ is not normally dangerous. You may not even feel it. It is not the voltage that causes danger, but rather the current it generates through your body. Anything over about $10mA$ will be unpleasant, above $50mA$ it gets dangerous. The current is determined by both the voltage and the resistance of the body. That resistance depends on how you touch the ...

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Now my question: Does this make sense? No. Or is it just esoteric hocuspocus? Yes. I didn't watch the video but read the text. Before mentioning the mechanism they tell you about their patents to make themselves seem legitimate. (first "red flag".) They claim that their product work by harnessing Earth Energy. "Earth Energy is electromagnetic ...

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