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15

The potential difference between two points on a wire carrying a current is given by Ohm's Law, $V = R\cdot I$. Since wires used for long-distance power transmission have, by design, a very low resistance per unit length, and the distance between the two extremities of your hands is very small (~10cm), even for large currents the potential difference is ...


13

It is, in fact, a double integral! The first notation used $$\varPhi_E = \oint_S \vec{E} \cdot \mathrm{d}\vec{A} = \oint_S \vec{E} \cdot \hat{n} \ \mathrm{d}A$$ is simply a more compact notation. It's much easier to write $\mathrm{d} \vec{A}$ instead of, say, $r \ \mathrm{d}r \ \mathrm{d}\theta$ all the time. Furthermore, it's more general, as $\mathrm{d} ...


13

Here is a circuit representing the system. $R_{wire}$ is the resistance of the section of wire between the bird's legs. $R_{bird}$ is the resistance of the bird (which you can measure by sticking the two probes of the multimeter to the bird's two feet - if the cable is insulated, you will have to add the resistance of the insulation as well). When the ...


5

I suppose you could view your situation as a circuit with two parallel resistors; those are a part of the cable and the bird. However the resistance of the cable is many orders of magnitude smaller than the bird's (the cable is effectively a short-circuit), so there won't be any appreciable current through the bird.


4

Thare is only one node connecting elements B, D, E, and G. The dots on the diagram are just to indicate that the lines do in fact connect, so that all of the wires are part of the same node. In this kind of schematic diagram wires are considered as ideal, and all points on the wire are considered to be at an equal potential.


3

Think of it in terms of current, V, W, and Z are in series, so each is equally bright. X and Y are in parallel, so each gets half the current of the others. If you assume each bulb is a constant resistance R (not true for incandescent bulbs, by the way), then V,W and Z will each dissipate $i^2R$. For X and Y, since each has a current i/2, the power will be ...


3

Earthing something means dumping the electron flow into the earth. Since the earth is so big, it can absorbe/give a practically infinite amount of charge without changing potential, this means that you can treat earth as a reservoir of ready to use electrons. If you plug the phase of your home power line into the ground (without safety devices in the ...


3

The switch really has 2 positions: on and off. However, when you move the switch very slowly, it may leave the closed position slowly. When the switch is just barely open, the field may cause the air to break down and start conducting, to form a spark (as @anna v explained). To rephrase, the reason why sparks happen is because the switch may only be open a ...


3

The general formula is indeed a double integral, so the most technically correct way to write it is $$\Phi_E = \iint_S \vec{E}\cdot\mathrm{d}^2\vec{A}$$ But when formulas start to involve four, five, or more integrals, it gets tedious to write them all out all the time, so there's a notational convention in which a multiple integration can be designated by ...


2

Yes, it is possible. The simplest qualitative answer to this is that, at the microscopic level, the electrons in a conductor are dictated by quantum mechanics, which is inherently probabilistic. Velocities and positions are rarely ever totally excluded from a given value; it's just insanely unlikely for a single electron to attain that given value. ...


2

The electrical conductivity of the water depends on the water temperature : the higher the temperature, the higher the electrical conductivity would be. The electrical conductivity of water increases by 2-3% for an increase of 1 degree Celsius of water temperature. Many EC meters nowadays automatically standardize the readings to 25oC. While the electrical ...


2

Yes, magnetic flux can be negative. It just depends on where the field is going. Say there is a sheet and magnetic field is going through it from front to the back, we can call the flux there as positive and negative when it's the other way round. It is pretty clear from the statement of Lenz's Law why the emf defined is taken as negative: An induced ...


2

Air is a bad conductor up to a certain value of the field generated by charges and the distance between them. After that air breaks down and a discharge happens, i.e. sparks. So below this level charges can accumulate by rubbing for example , positive ions left on one surface and negative on the other. When brought close a spark occurs. Why does holding ...


2

Yes , that's easy because mAh is presented for a specific voltage that battery can output. Because the battery must output at a specified voltage. Your 5600mAh is for 5 volts. If it's not 5 volts. You must recalculate it. But the voltage shouldn't be change if the battery is not adjustable. Hope you understand


2

The pairs of lines are the same phase and at the same voltage - they are really just a single thick wire split into two thinner ones. It is easier to install two smaller wires to double the current capacity than a single thicker wire. It is easier to handle the lighter cable and you can stock just a single gauge of wire and handling equipment. It also ...


2

Three-phase has two main reasons to exist: Driving N. Tesla's polyphase induction motors used throughout industry. Reducing the total cost of metal in cross-country power lines: w/single-phase lines, more metal would be needed to transfer the same rate of kilowatts. You're right: lighting as well as AC motors will briefly turn off at 120 times per second ...


2

John Rennie's answer is correct for a DC series connected motor and, almost certainly, this is the kind of motor you (the OP) are talking about. An interesting way of writing John's answer "backwards" is that you have just observed the reason why the most powerful traction motors are exactly this kind of motor - almost all DC train and tram motors are ...


2

When a motor is turning it acts as a generator and produces a back EMF that opposes the applied EMF. See my answer to Top angular speed of electric motor for more on this. A frictionless motor would draw no current when not under load, though obviously real motors do draw some current because of frictional losses. If you load the motor you reduce the back ...


1

The answer depends on the circumstances: how do you change the resistance? Both the drift velocity and the number of available charge carriers can be changed. In a basic Drude model for electrical transport both, $n$, the charge carrier density and $\tau$, the time between collisions determine the resistance: $$\mathbf{J} = \left( \frac{n q^2 \tau}{m} ...


1

Your understanding is correct. From $V=IR$ if voltage stays the same while resistance is increased, the current should be decreased. But if you have heard of another equation $I = \frac{Q}{t}$ If current(I) is increased and the charge $Q$ is fixed (Charge is fixed if the power supply is from power cells like battery). Time will be decreased. Which means ...


1

The whole (pedagogical) point of the slide wire generator is to illustrate that not only do changes in the magnetic field generate current in the loop, changes in the area of the loop - in a constant magnetic field - also generate a current. It's the change in magnetic flux that matters. As long as the wire is moving with some velocity, the magnetic flux ...


1

I found out that they mention about whole ions being moved in the human nervous system in order to transfer an electric impulse Electric impulse I think u mean signal. Take look on Action potential there picture demonstrates moving of signal. So neural signals are not current itself, or moving ions from head of neuron to his tail(transferring ...


1

The key to electricity is that it is moving charge. In our electrical wires we use electrons, which carry charge, to send signals. The current is the net flow of charge through a wire (or whatever is carrying the current) which then depends on the speed. The speeds at which electrons move involve a few distinctions. Firstly, the electrons move randomly due ...


1

magnetic flux linkage is negative A good observation. Now, the magnetic flux associated with a $surface$ is given by $\iint{ }{ }\vec{B}\cdot\hat{n}\mathrm{d}A$ The surface could be an open one or a closed one. Let us consider an open surface as shown below For an open surface, the area vector could be in any direction ( I've chosen an arbitrary ...


1

Magnetic flux is a scalar quantity and its positive/negative sign indicates the direction of the magnetic field. And the Faraday's law of induction is a quantitative version of Lenz's law, which may help your understanding: $\oint_{\partial \Sigma} \mathbf{E} \cdot \mathrm{d}\boldsymbol{\ell} = - \frac{d}{dt} \iint_{\Sigma} \mathbf{B} \cdot ...


1

The work required to move a charge $q$ between two locations $a$ and $b$ with a voltage difference $V_{ab}$ is $$w=V_{ab}q.$$ Differentiating with respect to $q$, one obtains $$\frac{dw}{dq}=V_{ab},$$ which is how the book got the equation. Basically, the intuition is that voltage is "work per charge moved".


1

I see you edited the question from a sauna to what I assume is a insulated test chamber. Steam would have very little change in the voltage required to getting a spark. You would also need more than just a bare wire, you would need a grounding plate inside your chamber. The voltage would primarily be a function of the air gap separating your wire and your ...


1

While DumpsterDoofus is right, perhaps this explanation might be helpful. A dipole is an asymmetric separation of charge, like this: $+ -$. A dipole can have many charges. The total charge must be 0. The center of charge for the $+$ charges and the center of charge for the $-$ charges must be at different places. A dipole can exert electrical forces on ...


1

but when they are pushed in the same direction, they create what we call an uniform electric field Movement of electrons in the same direction does not create a uniform electric field. Two infinite parallel plates with an electric potential difference between them, and no movement of electrons or other charged particles, would set up a uniform ...


1

In theory, provided that the surface area of the electrode remains constant and that the electrode material is conductive, the capacitance will not differ significantly when using different metals. This is just a consequence of the fact that for parallel plates, the capacitance only really depends on plate surface area. However, for modern electrochemical ...



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