# Tag Info

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, ...

3

Power is an instantaneous concept. $P=IV$ gives the instantaneous power at a given instant of time, given $V$ and $I$ at that time.

3

The "derivation" you describe is valid at a particular moment in time. \begin{align}\Delta E &= V \Delta Q\\ \frac{dE}{dt} &= V \frac{dQ}{dt} \\&= VI\\ P(t) &= V(t) I(t)\end{align} I added the dependence on time explicitly. To address your comments: $W=QV$ is only true when $V$ is constant; you can't simply take the derivative and ...

3

If you count the number of times the switch is flicked, then when the number is even, the lamp is off, and when it's odd, the lamp is on. So we can rephrasing your question: is infinity even or odd? That's one for mathematicians... they will probably say "both". So the short answer is - there is no "real" answer to your question. But most likely the lamp ...

2

I think you might consider first special relativity. We can model the problem as being in Minkowski spacetime with cartessian coordinates and put the switch at $(0,0)$ and the lamp in the coordinate $(0,L)$. Where $L$ is the distance from the switch to the lamp. Then the question is what is the state of the lamp at $(120,L)$? Using a spacetime diagram ...

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 ...

1

Yes, it is the electron kinetic energy gained between collisions with the lattice atoms which is transferred to the lattice atoms who heats the lattice. After collision the electron changes it direction essentially, so the drift velocity is small whereas the instant velocity is high. The drift velocity has nothing to do with the temperature. In absence of ...

1

my main question is, if the energy is not the kinetic energy of the electrons, what does in fact bring energy to the resistor and how does it heat up? We assume steady state operation. The drift velocity of the electrons entering the resistor must equal the drift velocity of the electrons leaving the resistor. This follows from the fact that the ...

1

First, for simplicity, assume the diode is ideal. For an ideal diode, the voltage across cannot be positive (the voltage at the anode is either equal to or less than the voltage at the cathode). Since the cathode of the diode is connected to the 0V reference, and since the anode is connected to the output node, it follows that the output voltage cannot be ...

1

I think that the 3 mA flows through the 3k resistor only - because that gets me to the answer you gave. The approach you need to take is this. The same voltage (3 mA x 3 k = 9 V) exists across the 3k and 6k resistors. You know the current through the 3k, so you know the current through the 6k (9/6k = 1.5 mA). Then you know the current through the 2k (1.5 + ...

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, ...

1

Simply put, does the voltage drop on each resistor mean that there are more electrons on one side of the resistor compared to the other side? Yes, the charge density at one end of the resistor must differ from the other if there is a current through. Consider, for simplicity, a resistive element of length $L$, area $A$ and resistivity $\rho_r$. ...

1

"a circuit that has different resistors at extremely different temperatures" -- Each resistor independently puts out its own noise related to its own temperature. "one long resistive element that has a temperature gradient across the whole thing" -- That's actually the same thing again. Treat it as a large number N of resistors in series, each with ...

1

Circuits with inductors are sensitive to changes in the signal - think of them as differentiators. Circuits with capacitors are responding to the integral of the signal over time. When you first turn on a circuit, the current wants to make a step change - which the capacitor doesn't care about, but the inductor resists vigorously. Thus the current will flow ...

1

@Floris' answer being good, i'll give another view on the matter. A capacitor is equivalent to an open circuit (since simply put, a capacitor is an element consisting of two plates which do not actually touch but through another medium, the dielectric, the circuit is not connected at that point where the capacitor is located), whereas an inductor is ...

1

Why is it so? Well, it isn't actually always so. It will depend on the actual circuit configuration and whether the switch opens or closes when $t=0$. But first, here are a couple of crucial results to always keep in mind when solving these type of switched circuits: the current through an inductor must be continuous the voltage across a capacitor ...

1

It is very simple, to pass current, it needs a path to follow unlike voltage (potential) which you can have with an open circuit. Think of it this way, electrons need to jump from atom to atom, this will happen until it reaches an end to the wire or conductor. At the end of the wire that ends, the electron stop and build-up to the highest voltage it can ...

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