New answers tagged

0

Poiseuille's law will tell you that a pipe of 0.1 m diameter will achieve a flow velocity of around $v=0.1\mathrm{~m/s}$, which is actually more than I expected. For pipes a bit wider than this, the flow will be turbulent (Re>2200), for which you can't apply Poiseuille. The interesting part is to what extent Poiseuille's law can be applied to such a system. ...


0

Because potential exactly means that you have its potential at every point and to get from start to finish you need to make a number of steps. That is one leap can be broken into a series of steps, every step is closer to the target. As you move closer to the target, your potential becomes closer to the target potential. That is, you have some potential ...


2

This answer has been hinted at in the others, but it's worth stating their collective knowledge as a succinct one liner that every physicist should know: Electric and Magnetic force only make sense in the light of special relativity if they are unified because if they were thought of as separate entities, then relatively moving observers would reach ...


1

The answer is that it depends on the field on the outside (boundary conditions) and the dielectric constant of the insulator. For a imaginary insulating sphere of vacuum in a vacuum, it should be obvious that the sphere does not affect the electric field at all. Inside a dielectric, the field will be weaker than on the outside. For a dielectric sphere in a ...


6

Several answers have given a physical explanation as to why electric and magnetic forces are tightly coupled, and why you can't develop independent theories of "just electric" and "just magnetic" fields. Your subquestions (especially #1) make me think you're looking for some kind of symmetry. It turns out, there's a really nice one! All the asymmetry ...


0

Power does indeed equal V*I, but the "more correct" form of the equation should be Power = delta-V * I. The power used by a circuit component is related to the voltage drop across the component, NOT the absolute voltage that the component is experiencing. Second point: the transmission of electrical power is done in a way that minimizes losses in the ...


3

The classical electromagnetic effect is perfectly consistent with the lone electrostatic effect but with special relativity taken into consideration. The simplest hypothetical experiment would be two identical parallel infinite lines of charge (with charge per unit length of $ \lambda \ $ and some non-zero mass per unit length of $\rho \ $ separated by ...


0

Let say the power produced by a transmission company is 50 Giga_Watt(we can take any value really). What happens is, they convert this to very high voltage.When you use a 1 kilo_ohm resistor, the current draw should be 22 amps, but the power generated(50Kw) must be kept in mind! You cannot have a power source of 10 W and expect it to provide 10 Volts at 2 ...


19

The arguments from special relativity given in the other answers is correct. What is charge according to one observer is current according to another observer that is in relative motion to the first. But this is, from a historical perspective, somewhat backwards. This consideration is what led Einstein to develop special relativity -- the paper is called On ...


80

Consider this: A charged particle at rest creates an electric field, but no magnetic field. Now if you walk past the charge, it will be in motion from your point of view, that is, in your frame of reference. So your magnetometer will detect a magnetic field. But the charge is just sitting on the table. Nothing about the charge has changed. Evidently ...


4

Regarding 1) observe that there is a pattern in common - namely that there is some region (volume for Gauss and a surface for Ampere) and integral of the source on this region is equal to the integral of the field on the boundary. This is a striking similarity. 2) currents are nothing else than moving charges. So both fields are generated by charges. These ...


8

You are right, the electric field and the magnetic field are distinct fields that have different properties. The reason why they are still classified as the cause for the "electromagnetic force" are the following: In higher theories, like the field theory, the electric and the magnetic field are caused by the same gauge principles. There is just "one" ...


0

Another way is to use fluctuations caused by solar flare coronal masses impacting on the Earth's magnetosphere, which give rise to magnetic storms. These can induce large currents in long conductors such as power grids. However, they are far more destructive than useful. On a more practical note, if you could turn the magnetic field of the Earth into ...


1

Using Gauss' law and the condition that there can be no electric field inside a conductor the initial charge distribution is as follows: $+2Q$ charge on the outside of the inner sphere. $-2Q$ charge on the inside of the outer sphere ($-Q$ original charge and $-Q$ induced charge) $+Q$ induced charge on the outside of the outer sphere There is an electric ...


0

She tried touching the machine in various places, again nothing. I inadvertently touched her hand while she was touching the machine and then suddenly she felt it too. From this it is evident you were a good conductor to the ground. You later say : We came back out 15 minutes later after drinking our hot chocolate and tried to reproduce the ...


0

Salt water is an excellent conductor. If you were still damp, and if the machine were broken in the right way, the salt water on your skin and slippers may have provided a route for a charge to flow to ground. Your wife with dry shoes, and you after drying out in the shop wouldn't.


2

Their average speed would be non zero but their average velocity would be zero as long as they are not moving preferentially in one direction.


1

The resistance of the wire is a function of the area and the length: $$ R=\rho\frac{l}{A}$$ Before you wind the wire it has a length of $10m$ and a cross-sectional area of $1mm^2$. After winding the wire around the wooden cylinder, it looks like this: So now it has a much shorter length, and the area is the cross-sectional area of a hollow cylinder. You ...


0

Your confusion is justified since the value of the work function depends on the configuration of the atoms in the material, and therefore can vary significantly. The work function values can be found in this Wikipedia article. I also have the 1975/1976 edition of the Handbook of Chemistry and Physics which contains a table of work functions, and separately ...


1

The essence of what you described lies in Maxwell/Faraday's equation: $$ \nabla\times\vec E = -\frac{\partial \vec B}{\partial t} $$ Which indeed implies that an electromotive force is induced in a time-varying magnetic field. This induced current follows Lenz's law, which states that the current generates a magnetic field that opposes the change that ...


2

I assume the "infinite energy" you're wondering about is electrical energy from current induced in the huge circulating rotor. As soon as you get an induced current there will be an induced magnetic field that will interact with the huge magnet and oppose the motion of the coil. Ask Heinrich Lenz all about it.


16

Oscillating does not always mean vibrating. Oscillation simply means some measurable value is cycling back and forth. This could be a vibration, which would be a measurable change in position, back and forth (like a grandfather clock or your phone's vibrator), but oscillation is a more general concept. For example, in linguistics, we talk of oscillation ...


7

Some components such as resistors, most (but not all) capacitors, and semiconductors aren't very prone to vibration. Other components like transformers are and have to be constructed to prevent audible vibrations. Back when CRTs were very common, it was not unusual for the coil(s) in their flyback transformer to loosen over time and cause a high-pitched ...


1

The electric field due to the outer cylinder has no contribution inside. One way to view it using Gauss's law, the other way is that if you took a slice from that cylinder, and considered a point inside it other than the center, you'll find a point producing electric field in the near side of the point (small charge, small distance) and a corresponding arc ...


2

The electric field between the conductors is due to both sets of charges. however when finding a value for the electric field using Gauss's law it is only the charges inside the surface which are of interest and it is easier to choose the charge on the centre conductor and the red Gaussian surface $S_+$ which would be a cylider. You could find the ...


0

the concept of generating electricity from magnetism is that a moving magnetic field produces an magnetic motive force gives rise to the electro motive force to the electrons of the wire which is being induced and hence results in production of electric current. But really don't you think this is a childish concept the whole process is about absorption and ...


0

You have to think in terms of potential . Consider the first plate, say $A$. It can be charged to a maximum value $+Q$ since any further increase in charge will cause a leakage of charge due to the increase in potential. You can imagine that. The potential of a charge distribution decreases slowly than the electric field with distance. So we need no leakage ...


2

The magnetic force acting on a charged particle doesn't affect the particle's energy. Otherwise magnetic forces cannot do work. It's because the magnetic force equation is given by $$\vec{F}=q\vec{v}\times\vec{B}$$ where $q$ is the charge, $\vec{v}$ is the velocity and $\vec{B}$ is the magnetic flux density. So, it is clear that by virtue of the ...


1

It might help you answer the question if you have some idea about the dimensions of a heater and of a light filament? Common types of electrical heaters have a helical coil of resistance wire wound on an insulated former as in the top diagram. The diameter of the helix might be about 1 cm and its coiled length about 30 cm. The light bulb has what is called ...


0

As I read your statements, I get the impression that the difference between capacity and capacitance is not clear to you. The capacity of a capacitor is defined by its "physical" construction (length, width, area, volume, material, etc. C = kA/d). However, capacitance is a measure of how difficult/easy it is for a capacitor to store charge (C = Q/V , ...


1

If you add more resistors in series the effect will be the opposite of what you say: the battery will last longer. A battery has a certain rated capacity, written in mAh (milliamps times hours). Divide this capacity by the current you are drawing and you will get how much will that battery last in hours, at the same current draw. More resistance means less ...


0

The neutral hole as you call it is actually a ground that connects to the body of the appliance being used. In the good old days refrigerators, for example, might develop a short between the internal circuitry powered by a 2-prong plug - by placing a second ground wire in the system which connected to the body of the appliance this "shocking" capability was ...


5

What you are hearing is mains hum: mains electricity is alternating current (ie the voltage is approximately sinusoidal and symmetric about zero), with a frequency of 50Hz or 60Hz. things like kettles and heaters use a lot of power and parts of them will mechanically change shape at this frequency, which is audible. This kind of physical noise from things ...


0

A split-ring commutator is basically a current reversing "tool" used in electric motors. A typical picture of the parts of a motor looks like this: As you can see the commutator consists of two round copper pieces. A piece of graphite is lightly pushed against the copper to conduct the electricity to conduct to the armature. It's often called a carbon ...


0

Electrons have a drift velocity which is very small. But electrons pass the charge. They do not flow with a charge on it. It's like dominoes that fall. The energy wave propagates through the falling dominoes, but the dominoes don't translate much. Also it doesn't matter who is propagating the charge. Electrons and protons and charged ions- all can do that. ...


1

The simple answer is that different people have different pain thresholds Your gender, your stress level, and your genes all contribute to your sensitivity to pain.


1

All the above ranges of the given electric current is in A.C. Hence, even 1 milliamp of a.c. current is dangerous for us. The reason for this is that our body has a capacitive property which lets the a.c. current to pass through us and we fell a shock even at a very low current. But d.c. current of 1mA or even 1A don't appear to be dangerous. All this is ...


2

I would say it is both! Because of the abundance of electrons, the electric field at the battery pole/boundary, at the instant of turning on the switch (t=t0), is quickly (within a few Debye lengths) screened and cannot possibly reach the electrons further down the wire. However, the electrons at the vicinity of the pole that do feel the effect of electric ...


1

You're not the first, nor the last, to find the phrase "power flow" somehow wrong. For example, from W J Beaty's article on electrical misconceptions: ELECTRIC POWER FLOWS FROM GENERATOR TO CONSUMER? Wrong. Electric power cannot be made to flow. Power is defined as "flow of energy." Saying that power "flows" is silly. It's as silly as saying that ...


0

Well, if you think about electric power, which includes current (notion of flux), then you'll end with the conclusion that if there's no flow, there is no power.


0

It is not generally realised that "internal resistance" is a myth which cam be evaluated only by practical experiment and calculation using Thevenin's theorem. But that does not mean that it is a useless concept. Indeed it is essential for design in ALL branches of engineering. For example a plumber measures the efficincy of a water-supply by measuring ...


4

An easy way to determine whether there's current passing through the person or not is to look at the voltage difference between the two points that this person connects to the circuit. Because the difference in voltage is the reason of current passing through. (Same as no water pressure difference, no water flow) When touching a wire with two hands, because ...


1

In addition to Zeeshan's answer, if you consider there is almost zero resistance between the points our hypothetical man is gripping, then there is no difference in the electrical potential between those two points. There is, therefore, no electromotive force (voltage) to drive a current through the man's body.


2

The man will NOT die in both the cases. Lets see it from the perspective of current. Imagine that you are the current travelling in the wire. You have to move from point A to point B (Let A and B be the position of contact of the man's hand with the wire) . You have 2 choices. First, you can go through the wire with low resistance to stop you. Second , you ...


1

UPDATE : John : Thanks for data. Graph is ok. I note your intercept is E=3.94V but your calculations use E=4.5V. This explains the discrepancy in your results. If you use 3.94V you get r ranging from 1.59 to 1.76, close to slope value of 1.68 Ohms. ORIGINAL ANSWER : Your line of best fit gives an average internal resistance r based on all measurements. ...


1

For instance, why don't measure the ability to store something by the volume it takes so why not charge per unit volume. There is nothing wrong with you defining a parameter which is the "charge per unit volume" but after defining it then what are you going to do with it? So here you have a capacitor and its charge per unit volume is $3 \;\text{C ...


2

I understand that capacitance is the ability of a body to store an electrical charge and the formula is $C = {Q \over V}$ Perhaps you just need to top thinking of capacitance as that. "Capacitance" sounds like "capacity", which leads to an intuitive trap like this: If I have a basket with a capacity of 2 apples, then a basket with more capacity can ...


3

We Use $C=Q/V$ because those were useful things to measure. It's often easy to forget, but many of the equations we use are chosen because the work, and because other equations didn't work. Never underestimate that part of the reality. We don't use "charge per unit volume" because that number is not constant. You can charge a capacitor up without ...


3

This question appears to be a pseudo-duplicate on the Skeptics exchange, as pointed out by @CraigGidney. The highlights of the comments here and answer there appear to be that: 1) Yes, one could potentially accrue some electricity from soil. 2) No, it would not (ever) be sufficient to charge an iPhone, let alone 3 times. 3) In the comments here, "there ...


23

You can use a high vertical tube to store water in it (fill it from the bottom by pushing the water in) How much water can you store? It obviously depends on the pressure you apply to push it in. If you push harder, there will be more water stored. The tube is characterized not the amount of water, but by how easy it is to store the water. Its "capacity" ...



Top 50 recent answers are included