# Tag Info

42

In addition to the other answers, here is something for the intuition: $$V=RI$$ More "pressure" $V$ (more correctly: higher "pressure" difference from one side to the other) is required to keep the flow $I$ of charges constant when the flow is resisted by $R$. A thin wire has higher resistance than a thick wire, $R=\rho L/A$) analogous to a "bottleneck" ...

17

Start with the initial diagram, but let's color code everything: Now move some wires around, without actually changing the connectivity: Finally, rotate the left and right blocks while again not changing the connectivity:

17

In a superconductor, the current can keep flowing "forever" since there is no resistance. But since conductors have inductance (in fact, superconductors are used most often to create magnets like for an MRI scanner), applying a voltage would not (immediately) cause an infinite current to flow. It is instructive to see how an MRI magnet is "ramped" (turned ...

13

Another term is thermal resistance, This is incorrect. Thermal resistance is something that prevents heat flow. It is an entirely separate concept from electrical resistance. How is contact resistance explained? To obtain very low resistance in a material like most metals, the electrons must be delocalized from the individual atoms, and free flow ...

10

Short answer - yes, everything in the circuit can contribute. But usually, an ohmmeter is zeroed with the probes in place - in other words, whatever resistance the probes represent is taken out by the meter. There are two other factors that play a role, especially when you try to measure small resistance. The first of these is contact resistance: it is ...

9

Think of plumbing for a close analogy. Voltage is how hard you are pushing, and current is how much flows. The relationship writes itself: why would you get more or less flow from the same pump? The measure of how much effort is used to get flow (it makes more sense as the reciprical: how much flows for a unit of effort) is the interesting property, and ...

8

If you have an excess of electron in your body, your hair might stand on end and you might feel a bit negative (I couldn't help that pun), and you should probably avoid touching people or metal object if you don't want a static shock, but other than that, it's mostly harmless. The real danger comes from flowing electrons. Because the body basically runs on ...

7

Have you looked at Drude's model? I was taught something like that back at school and have kept it in mind as a intuitive way of understanding it. We want to understand why the current (rate of flow of charge) should be linear with the potential difference. The Drude idea is, as you noted, related to friction. Firstly, the EM field is linear in the ...

7

There IS a potential, and all three bulbs will be on. First, you need a reference point to measure voltages. Let's take the wire right of the right battery, and define its potential as 0V. If both batteries generate a voltage of 5V, the wire between the batteries will have a potential of 5V, and the wire left of the batteries will have 10V: So, bulb 1 ...

6

A battery connected to a capacitor is an RC circuit in the limit $R \to 0$ (i.e., there is no resistor and the resistance of the wire is negligible). One might think that the energy loss is zero in this limit, but this is not the case. For an RC circuit with a battery and an initially (i.e., at $t=0$) uncharged capacitor, we have Q(t) = CV ...

6

If they have 0 resistance then I (V/R) should be infinite? According to Ohm's law, the voltage and current associated with a conductor are proportional: $$V = R \cdot I$$ where the resistance $R$ is the constant of proportionality. This equation holds for an (ideal) ohmic material. We can rearrange this equation to be $$I = \frac{V}{R}$$ except ...

6

Typically this is explained by the saying, "current kills." It's not the charge (or potential above ground) that a body attains that hurts biological systems, it's the current that flows through them and either 1) heats them or 2) disrupts important electrical signals in the body. Heating damage occurs and can "cook" (cause 1st, 2nd, or 3rd degree burns ...

6

The instantaneous power expended in a resistor is proportional to $V^2$ (i.e. independent of its direction), so the average power expended is given by the mean square voltage! The square of the average absolute voltage will not yield the power expended in the resistor. Edit: And actually this close-to-duplicate question does have more extensive answers ...

6

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 ...

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, ...

5

When the switch is opened, the circuit is the equivalent of this, so I think you can clearly see that the resistors are in series and so are the capacitors. It seems that you already understand how to calculate series resistance, so I'll show how to understand series capacitance. First, you probably already know that capacitance is defined as the ratio ...

5

If you go in depth of resistivity, it will be easy to get through the point. Voltage is the reason for the movements (flow) of electrons that produce current (charge divided by time). If you have many electrons and atoms in the way (like barriers, like when you are running in a crowd!) they reduce the rate of charge flow. Now it is clear that if there are ...

5

If you set up a circuit with any component (not just resistors) connected to a voltage source, you will find out that the current which will flow through the component depends on the voltage. In most cases, the higher the voltage the higher the current you will get. Conversely, you can ask: how large a voltage does it take to get a certain current through ...

5

The voltage is zero. That's the point. The main way current gets started, like in an NMR magnet, is by inductive coupling.

5

This is a very interesting question, especially considering the very recent history of scholarship on electrical contact resistance (a term first coined in 1964 by William Shockley, one of the inventors of the transistor), as well as thermal contact resistance. For the following explanation, I will use this research paper on electrical contact resistance ...

4

I understand also that there would be a tiny minuscule resistive loss through the wire, but really it's not enough to say anything about. On the contrary, it's crucial. Assuming an ideal voltage source (can supply unlimited current) of voltage $V_S$, an ideal resistor of resistance $R$, and an ideal uncharged capacitor of capacitance $C$, are ...

4

A study undertaken by Nutting and Nuttall at the University of Leeds found that "gold is not inherently more ductile than other face-centered cubic metals", such as copper. The authors found by experimentation that "gold is considerably less ductile in tension than silver." But when beaten foil becomes very thin, other metals tend to fragment, whereas gold ...

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 ...

4

Use kirchoff's loop and junction law. :)

4

know that the two conversion coefficients are close but I simply cannot see why the RMS value is the one that conforms to reality. It's true that we can ask for the average of the magnitude of a sinusoid over time and calculate it. This is a useful quantity if, for example, we want the time average voltage at the output of a full wave rectifier ...

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

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 ...

3

When you insert a third conductor between two plates of a capacitor, you essentially create a three-plate capacitor. The usual way to obtain the static solution (capacitors with general arrangements of the plates) to such problems is to assume the conductive materials are ideal conductors and use a numerical method such as finite elements to solve ...

3

Let us crudely imagine the voltage source as a pump pumping water up to the top of a water slide, and the resistor as the slide itself with water flowing down through it. The height difference between the top of the slide and the bottom of the slide is the same as the height difference between the top of the pump and the bottom of the pump. The voltage ...

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., a difference in the number of electrons. Now, if ...

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