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1

Actually, we don't know that "filament bulb has straight Volatage vs Current graph": "The actual resistance of the filament is temperature dependent. The cold resistance of tungsten-filament lamps is about 1/15 the hot-filament resistance when the lamp is operating. For example, a 100-watt, 120-volt lamp has a resistance of 144 ohms when lit, but the cold ...


2

Since I understand that power = V x Current, the power for a bulb can not be a constant if its resistant is assumed a constant. A normal mathematical thinking can confirm that. If the voltage and current don't change, then the power is constant. The electricity supplied from the wall is at 115V (more or less). If the resistance of the bulb is 1322 ohms, ...


2

The power rating given on lightbulbs always refers to the power at a specified operational voltage (which is always given together with the power or implied by the type of socket). The power at different voltages is not easily predictable as the resistance of the filament will vary strongly in dependence of temperature (which depends on the dissipated ...


0

Even if the circuit has no resistance(which isn't possible as every wire has some finite non-negligible resistance $\rho L /A $), the source will have some internal resistance causing the circuit to have resistance, after which you can use Ohm's law to find the current. Though it isn't recommended to connect two ends of a battery together.(It reduces the ...


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if you were to have say a 5V source connected directly to ground, no components in the circuit at all, you would need to add resistance for the current to flow? No, for sure current will flow. If nothing resists the electrons, they will keep speeding up. Current $I$ will keep rising. Power will keep increasing, $P=VI$. For really no resistance, ...


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On AC a nice measure to take could be the effective current. Its definition is the following: The effective AC current is the current value such that the average power transfer would be the same on an DC current. So, power is therefore calculated: $$ P(t) = V(t)I(t) $$ For AC circuits where voltage and intensity varies with time, we have a varying power: ...


0

Incandescent bulbs appear dim because the filament's temperature is below it's design temperature. It's running cool because the current flowing through it is lower than normal. Current + resistance = heat for most non-exotic conductive materials. The current is lower than normal because the applied voltage is lower than normal. As a light bulb's ...


1

In short it's low voltage. Current, voltage and power are all linked via the impedance (like resistance) of the thing in question. The voltage is a property of the grid, with something like a light bulb you can assume the grid voltage won't change. it might if you were running an industrial induction furnace maybe, but not with a light bulb. The current ...


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You have most likely been measuring a voltage that was induced in the loop formed by the multimeter leads and your skin. Do the measurement again, this time just shorting the leads while forming a loop of similar area. If the voltage is still there, it has nothing to do with your skin. If you wanted to measure the electrostatic current from your body ...


1

Your oscilloscope is not triggering on the signal, the horizontal deflection time is set near a multiple of the period of the 50/60Hz wave and the instruments starts at slightly later phase each time it traces the waveform. That way the wave seems to move "backward" in time. If it starts tracing at a slightly earlier phase, then the wave seems like it's ...


2

In general, Ampere's law does not necessarily give the value of the magnetic field. It only gives the integral of the field along a closed path. That integral can sometimes be used to deduce the magnetic field at any given point, but only if you know something about the magnetic field from symmetry or other considerations. For example, along a circular ...


2

Ampere's law (for a steady current) states that $$ \oint \vec{B} \cdot d\vec{l} = \mu_0 I$$ If we consider an infinite wire, then symmetry tells us that the B-field at the point $A$ and all other points on a circle of radius $(R+y)$ is constant in magnitude and is in the azimuthal direction. Hence the magnitude of the B-field is given by $$ 2 \pi (R+y)B = ...


0

You only have an electric field if the current that passes is not neutral(i.e. it has more positive or negative charges in a unit length) or if the current changes with time. In the second situation,the magnetic field around the changes with time(so is the magnetic flux inside a "made-up" area around the wire),so nature causes an induced electric field in ...


1

As you can see from an example of electrodynamics book by Griffiths: For ANY wire,equation (5.35) still holds.And you can see that for an infinite wire,θ1=π/2 and θ2=-π/2.So,in your situation you can use only θ1 οr θ2 by changing the other angle to zero.It does not matter which angle you keep,mathematically,they will both give you a B of the same magnitude ...


6

A negative voltage means that you have hooked your power supply across your device backwards. Purely resistive devices, like resistors and lamp filaments, don't care which way current flows through them, only how much current flows. Such devices will always have current-voltage curves which are "odd" functions, with $I(-V) = -I(V)$, as in your graph. It is ...


1

Most resistive materials have a nonzero temperature coefficient: the resistance changes with the temperature of the device. An incandescent lamp filament, which glows because it is hot, might have an temperature of several thousand kelvin. On the other hand, if you probe the lamp with an ohmmeter while it is off, you'll typically use a current of a few ...


3

The resistance of a lamp filament is not constant. As the current increases and the filament heats up the resistance increases. That's why the statement you quote is phrased that way. It means that the resistance is 4 Ohms when the current is low enough that the heating and resistance change are negligable. More verbosely it could be phrased: The limit ...


1

Short answer: it depends on the impedance of the load attached to the secondary coil. A perfect transformer can be modeled as a pair of inductors with mutual inductance $M$ and self-inductances $L_1$ and $L_2$, with $M^2 = L_1 L_2$. Denote the voltage across coil 1 and the current through it as $V_1(t) = \tilde{V}_1 e^{i \omega t}$ and $I_1(t) = ...


0

It certainly affects life expectancy and if do it continuously at right intervals you can even destroy the motor/generator in a matter of few minutes: http://en.wikipedia.org/wiki/Aurora_Generator_Test When a motor/generator is connected to the grid it revolves in-phase with the grid. When you disconnect it, its frequency will change and its phase will ...


0

amp meters would not work as they display the instantaneous current consumption...what you need is to monitor the integral of i^2*R where R is the resistance of the water heater in Europe (UK or Germany), your electricity company would give you a so called smart meter. this has a clamp current sensor that can be connected around the power cable going to the ...


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imagine a small section of the conductor, say 1mm thick...indeed on the left side, there is a given amount of charge exiting this section, but from the right side, there is an equal inflow of charge. For that reason, the total amount of charge in the section of conductor does not change


3

You can think in terms of the current density vector. Its definition: $$ \mathbf J = \sum_i n_i q_i \mathbf v_i $$ Where $n_i$ is the charge carrier density in the media, $q_i$ is the charge of the charge carrier, and $\mathbf v_i$ is the average velocity of the charge carrier. Assuming we have several charge carriers (electrons, ions, etc), you have to sum ...


1

What's the effect of a resistor? It's a component that dissipates energy end thus lowers the voltage. So what is voltage? It's the strength of the field that moves the electrons, while current represents the number of electrons flowing through the wire. Free electrons can be stopped all together or slowed all together, but it's not possible to select only ...


1

On the one hand, you can't solve for the magnetic field without appropriate boundary conditions (e.g. there could always be an incoming electromagnetic wave that hasn't yet impinged on your cylinder). On the other hand if you have a fixed charge and current distribution you can always use Jefimenko's equations to find a solution to Maxwell's equations, and ...


2

I know that Wikipedia is not the best source for reference, but according to this page the superconducting parts that are cooled by liquid nitrogen in most cases. Most of the superconductors are High TC ones, which still needs to be cooled. Here are some links related to this topic: Toy train Video Paper on HTS (High Temperature Superconducting) Maglev ...


1

Laser Doppler velocimetry can be used. Generally it is used to measure velocity of this range for any transparent fluid flow.


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Vacuum tubes can conduct hundreds of amps of electricity quite readily. The effect depends on heating the negative terminal so that electrons can leave the metal surface which otherwise keeps them in the surface owing to a phenomenon called work function.


1

Resistance is directly proportional to the length of the wire, and inversely proportional to the cross sectional area of the wire. R = pl/A, where R is resistance, p is the material's resistance in ohms, l is the length, and A is the cross sectional area in m^2. As a wire gets longer its resistance increases, and as it gets thinner its resistance also ...


2

It is not that there is no "interaction" - at any point in space, the two magnetic fields will add up with the resultant pointing in another direction. In other words, the magnetic field caused by the wire will appear to distort the externally imposed field. However, this distortion is radially symmetrical: you can think of the magnetic field lines as ...


4

They are obviously talking about "conventional" current, not the flow of electrons. When you want to know the direction of magnetic force on a current you need to use "conventional" current direction. There is an interesting corollary to this relating to the Hall effect - if current in a semiconductor is carried by "holes" the polarity of the Hall effect ...


1

I understand the problem now from leongz's excellent explanation and patience in the chat discussion. Thank you very much leongz for helping me out! The capacitor is being discharged through constant current. If it starts with charge Q_0, then from the definition of current we know that the charge decreases by It after time t, where I is the constant ...


0

Any physical quantity, if it can be expressed as a function that has all its' derivatives at a single point, can be expressed as a Taylor Series


4

You don't need to use relativity to see what will happen in to a current in a gravitational field. We assume a wire of constant cross section with length in the vertical direction , and a constant current flowing through it. This must be done by applying an electric field $\mathbf{E}$ along the length of the wire, producing the current density (according to ...


1

Current is a measure of charge flowing in some unit of time. The gravitational field will dilate time. The current will be reduced in the observer's point of view. $I = V/R$. Since resistance is constant, this means that voltage must have decreased in the observers point of view.


1

Consider the left branch of the bridge. The total resistance is $P + Q$, so the current is: $$ I_{left} = \frac{V}{P+Q} $$ The voltage drop across $Q$ is just $V = IR$, so the voltage at the $PQ$ midpoint is: $$ V_{PQ} = V_{in}\frac{Q}{P+Q} $$ We argue in the same way for the right hand branch to get the corresponding equation: $$ V_{RS} = ...


0

Current is conducted due to loosely held electrons present in a metallic lattice. (refer metallic bond on wiki). Note the electrons are loosely held to the neucleus and they are not free to fly away. When a potential difference is applied across a metallic conductor these electrons move from low potential to high potential giving rise to an electric current ...


0

This is often referred to as the "step voltage". The image below illustrates the electric field. (it's caused by a wire and not by a lightning, but you get the idea) from here: http://commons.wikimedia.org/wiki/File:Potenzialtrichter_Freileitung.svg The problem of touching two points of the ground is that there can be a difference in the potential of the ...


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They are under the electric influence of the terminals. If they negatively charged, it will be attracted to the positive terminal.


1

The general answer is "yes". There is a current flow through the solution and if you put part of yourself into it then part of the current will flow through you. How much current is the real question, and that depends on a whole lot of variables such as voltage and current between the electrodes, their separation, where you place the biological component, ...



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