# Tag Info

83

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 ...

20

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 ...

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 ...

9

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" ...

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 ...

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 ...

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 ...

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 ...

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 ...

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 ...

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 ...

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 ...

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 ...

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.

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 ...

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.

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 ...

2

It is possible to have a perfect voltmeter: You can use a potentiometer with a current meter but you also need something with a standard voltage (standard cell, whose emf is larger than what you are trying to measure). It is a null method, that works by varying the sliding contact on the potentiometer until a zero current is registered. Zero current means no ...

2

As pointed out by the comments, it will cost more energy than what the turbine will generate... if the car is riding in calm weather without wind. But what if the car is driving at a velocity $v$ while the wind is blowing at a velocity $u$? The relative wind speed will be $w=u-v$. According to Betz's law, a wind turbine with a swept area $S$ and an air ...

1

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. For turbulent flow, you can look into the Darcy-Weisbach equation. The interesting part ...

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 ...

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 ...

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 ...

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 ...

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 ...

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 ...

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.

1

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 ...

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. ...

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