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1

But what about the 180° gap in the middle? This implies a negative real part of the impedance, i.e., a negative resistance. Express the impedance $Z$ in polar form $$Z = R + jX = |Z|e^{j\phi}$$ where $$|Z| = \sqrt{R^2 + X^2}$$ and $$\tan \phi = \frac{X}{R}$$ For $R > 0$ $$-90^{\circ} \lt \phi \lt 90^{\circ}$$ but for $R < 0$ $$90^{\circ} ...


0

If the phase angle is greater then 90 degrees the load would effectively become the source and vice-versa.


1

In 1999, the president of the IEEE Power Engineering Society, Robert Dent, noted that: "The degree or intensity of the corona discharge and the resulting audible noise are affected by the condition of the air--that is, by humidity, air density, wind and water in the form of rain, drizzle and fog. Water increases the conductivity of the air and so ...


2

I think EnergyNumbers's Answer is an excellent one, but could leave some people a bit mystified by what exactly a "direct ray" is and what exactly its relevance is. The essential idea here is that a Fresnel lens is an imaging machine: it puts a curvature on a low aberration wavefront so that that wavefront converges. Its working depends on there being ...


1

I think the range of answers you have got from friend, teacher and web reflect that there is not a straightforward response. Without high voltage it would not be possible to drive the dangerous current through the body, but high voltage itself is not lethal - it depends how much current can be delivered at high voltage. Another question is how high does the ...


0

They are not generally used with the photovoltaic cells as they concentrate the sun light and heat to a temperature so high that many of the cells get, for lack of a better word, fried.


1

Some corrosion always takes place (pure gold is not used for transmission lines, AFAIK:-) ), so the conductivity decreases with time, although for some materials this effect can be very small ...


2

The line itself does not change much over years. What changes and therefore needs maintenance on power transmission lines is insulators, connectors and spacers. Insulators get dirty or simply break, connectors work loose due to thermal expansion and contraction, mechanical stresses and oxidation, and spacers can be damaged by wear due to these same ...


0

"Stange" harmonics cannot appear. Two 50Hz sinus waves always produce another 50Hz sinus wave : $$cos(\omega t)+cos(\omega t+\phi)=2cos(\omega t+\frac{\phi}{2})cos(\frac{\phi}{2}) $$ About synchronization, you should remember that the voltage in the network is fixed, and thus only the current changes. I don't see any problem with combining two different ...


1

Cores of the transformers a made of ferromagnetic material, which can change the shape due to magnetostriction phenomena. When transformer works with typical grid frequency of 50Hz..60Hz, it can be heard. As it was answered above, generated noise depends on mechanical construction. New power supplies use frequency converters, which drive the transformers ...


6

Transformers generate oscillating magnetic fields at the mains frequency and the fields produce an oscillating force on: anything nearby that's ferromagnetic (like the core) anything nearby that is carrying a current (like the windings) The sound you hear is because various bits of the transformers are moving in response to the oscillating fields and ...


0

Current is basically the flow of charges.Well what i think so whatever charge it is it will flow and will cause the production of current and if there is a production of current electricity is automatically formed.For example the current positron generator.Here is a link where there is a PDF which is all about Dirac current generator ...


4

You are being imprecise about electricity. It's probably better to just think of electricity as current. You have a current whenever you have a charge moving. To your question, yes, positrons are just as good as electrons for carrying a charge. There is no difference between "positron electricity" and "electron electricity". Another way to see this is ...


1

The exact equations for I-V characteristics of transistors are derived using quantum-mechanics. Several approximations can be used, one of which is based on the shottky barrier analysis This reference here derives the I-V linear and quadratic approximation (in saturation) for FET transistors. Another reference here UPDATE: As @QMechanic pointed, ...


0

Situation 1., the ideal wire with an ideal voltage source, is an idealization: it is not a situation that can occur in nature. One should not be surprised that physics, which aims to describe nature, cannot describe a situation that cannot occur in nature. I will note that you specified a battery, not an ideal voltage source. In this case one can develop ...


0

The drift velocity does not depend on the length or the cross sectional area of the wire, when dealing with a macroscopic (ordinary, everyday life) wire. However, if the wire is, say, too short, e.g. comparable to the average distance a charge carrier travels before undergoing a collision, then it might begin to depend on the wire length, but for all ...


0

For simplicity, I'm going to assume a 0.7V diode drop in the ON state. In your diagram, you can call the low node ground (0V), in that case, you have one of two situations: The diode is on (closed switch) In this state, current can flow through the resistor and therefore, through the diode. In this case, 0.7V is dropped across the diode and the remaining ...


4

You are familiar with the concept of static electricity. When you have a DC line with many thousands of volts on it, there will be a polarizing effect, and that will attract things to it - especially dielectrics. Now if your piece of paper is thus attracted to the line, and you try to grab it, it is quite possible that you get peripheral nerve stimulation ...


0

The first expression refers to definition of polarization in terms of density of physical electric dipoles. The second expression refers to (approximate) physical law, which says the polarization is proportional to total electric strength.


0

In the first equation $\Delta L$ itself is typically proportional to $E$. That establishes the connection between the two formulas. However, $\Delta L$ might not be proportional to $E$. It might be permanent. The first equation allows for this case, but the second does not. If $\Delta L$ is permanent, the material has a permanent electric dipole ...


0

Electrons indeed move extremely slow.However it is not the really the electrons' motion for which the light goes on in a bulb as you switch it.Just as you find water coming out of a pipe as you open the tap (the water flows;the water at the mouth of the pipe comes out as you open the tap.Similarly the electrons push other electrons and so on and this ...


2

The first mistake is directly taking $dq=\lambda dy$. If you look closely, as you go up from the origin to higher y, you find that charge density per unit y increases. Take instead $\lambda$ as charge per unit circumference of the wire. i.e $\lambda={dq \over dl}$ = $\lambda={dq \over rd\theta}$ Now, $$dE= {k\lambda dl \over r^2} \cos{\theta}$$ ...


0

Individual electrons may have a range of speeds in a circuit (thermal motion, scattering, absorption, photon etc..) However the current (or drift velocity) gives the average speed of the whole electron cloud (not a single electron). Note again single electrons may have a range of speeds (from slow to very fast, near $c$). It is the electron cloud that ...


1

The speed of an individual electron cannot be c: an electron is a massive particle and can therefore never achieve the speed of light Furthermore, an individual electron moves very slowly in a current (mm/h scale). The question i think you're trying to ask is how fast do electric signals travel through a wire. (e.g. if I had two lightyears of copper wire ...


1

You've begun with this: $P_l = I^2R$ $P_l = IV$ This is correct, but the $V$ here is not the line voltage, but instead the voltage drop across the resistor under consideration. Increasing the line voltage does not increase the voltage drop. Your diagram with a single resistance and a power station implies that the current in the line depends on that ...


0

The diode has a central barrier at the PN junction which allows charge to flow across it only when a sufficiently positive voltage is applied to the P part with respect to the N part so that the barrier potential is overcome.In this case the diode is said to be forward biassed and conducts current.At all times when the P part has a voltage less than the ...


0

From the information you have put in your question I think that in the reverse bias case the 'diode is open' means that it behaves like an 'open circuit' or 'open switch' and no current passes through it and thus no current goes through the battery. The load resistor has current passing through it that goes to circuit/components not shown on the right hand ...


1

The pendulum motion can be converted to energy any number of ways. For example, if the pendulum bob is a magnet simply placing a coil of wire near it as it swings will induce a current which can be siphoned off and used.


0

Look, for example the page at http://farside.ph.utexas.edu/teaching/302l/lectures/node57.html . It seems that the EMF E is a characteristic of the cell. So it should be constant, whatever hapens that is non-destructive. Regarding the second question, both formulae are correct, and both refer to the same voltage V between the points A and B in the figure of ...


0

I'll try to keep it short and sweet; Stranded wire is capable of delivering high amperage without overheating because the strands devide the load..I.E. battery cables on your car. stranded wire is superior to solid but to expensive for long runs, so solid wire is used for long runs like for your house (easy to snake or bend) solid but flexible electric ...


1

But recall that power dissipated $P= VI$ is also , from Ohm's law, expressible as $P = I^2 R$ So the dependency of power dissipated is linear in voltage, but quadratic in current, given the same resistance. Also remember that the voltage supplied from the power station, and the voltage drop across the transmission line - which is what is important in ...


0

What you're likely seeing are the leafs returning to their natural, uncharged state. They are not attracting each other. Their close proximity is due in part to gravity, as you say, but also the particular shape of the supporting apparatus.


2

In addition to the good answers above here is something to think about. If the resistance is zero then for a current to flow there does not need to be a battery - the emf can be zero. No work is done as the current flows. This may sound like a strange case, but it is how many strong magnets work in nmr (nuclear magnetic resonance) spectrometers. The have a ...


6

Your original text admitted three interpretations, and I'm leaving the answers here: 1: What happens with a toy model when there's a circuit with an ideal battery and no resistance? All the charge moves around the circuit at one moment in time (infinite current). The energy must leave the system as Electromagnetic radiation - accelerating charges radiate, ...


2

Yes, there is a fundamental reason why electricity is so universal. It is because matter is made of electric charges bound together (protons and electrons). When you think of non-electric technologies such as the wheel, realize that the wheel relies on the rigidity of matter which depends on the bonds between atoms which are electric in nature. So even ...


1

You should be able to get the same result by using the electrical work formula - but note that you need to integrate since the force changes with position. That's really all the potential is - it is the integral of force for unit charge. That's why force has the $1/r^2$ relationship while potential has $1/r$ (with appropriate signs and constants...). ...


-1

Do not open the cone. Think of it in the profile view : You have an isosceles triangle. Now move along the axis of the cone, say a distance $x$ and take an element $\mathrm{d}x$. Somewhat like this : This small element is similar to the rectangle you described. With length as $2\pi r(x)$ and width $\mathrm{d}x$. You also know the velocity with which the ...


0

Others have provided mathematical explanations, so I'll try an intuitive explanation. You've probably seen the electric field represented like one of these: (image source) At the top of the mountain there is a positive charge, and at the bottom of the valley is a negative charge. A positive test charge in this field experiences a force analogous to a ...


3

As you said, current is like water flow similarly voltage is like water level and voltage difference like difference of water level. We know that water flow from higher level to lower level like current flow from higher voltage to lower voltage. Voltage difference means there is a difference of charge i.e. difference in number of electrons. Now we consider a ...


5

Suppose your pipes form a loop i.e. water can flow through the pipes and get back to where it started. As the water flows round the loop there will be some places where pressure rises (e.g. a pump = battery) and some places where pressure falls (e.g. a restriction = resistor). However if the water goes all the way round the loop back to its starting point ...


2

The Kirchoff Voltage law states that the sum of emfs in a circuit is equal to the total potential drop in the circuit. So for a simple example, where you a 6V cell, for example, and 2 resistors in series. The 6V cell can be seen as a place where the water is given potential energy - if we imagine a ramp, it would be the water being pumped up to the top of ...


1

AC can be made from DC, and vice versa. DC is a steady voltage, with AC the voltage fluctuates from negative to positive and back, many times per second. Most electricity generators generate AC. The reason for preferring AC is that, historically, it is easier change voltage with AC: all you need is a transformer. The generators generate a high voltage, ...



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