The study of the presence and flow of electric charge. Charges, currents, fields, potentials.

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Maximum power transfer proof

I have the following homework problem. Consider a power supply with fixed emf $ε$ and internal resistance $r$ causing current in a load resistance $R$. In this problem, $R$ is fixed and $r$ is a ...
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53 views

Can we create a electric field without actually using a battery or power source?

Can we create an electric field without actually using a battery or a source of electricity? Like a take 2 panels, one is positively charged and another is negatively charged and put them parallel to ...
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35 views

Electricity from electrons

If I was able to get electrons flowing through a glass tube what happens if I put wires connected to a bulb into that stream of electrons?
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72 views

Auto spinning turbine generator

This might be dumb question but I'm so curious to know if this actually works or is impossible. I was researching how you could generate electricity from magnets and copper wire and also have read how ...
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109 views

Computing energy loss for a hysteresis curve

Let a hysteresis loop be as shown in the figure, with $B_0$ the applied external field due to a current $I$ in a toroid, and $B_M$ the additional field due to the ferromagnetic material. Hence we ...
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21 views

How can DC-magnetic fields be produced with the aid of currents?

How can DC-magnetic fields be produced with the aid of currents? What's a possible theoretical explanation for this, and how does one achieve this in the real world? What are the maximum fields that ...
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73 views

Energy Loss during Sharing of Charge between two Capacitors

It is fairly easy to show that there is always a loss energy when two capacitors share their charge to attain the same common potential, but is it with the same ease that one can explain why it ...
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3answers
106 views

Why does the electric field vanish at infinity?

When $r \rightarrow \infty$, $E \rightarrow 0$ for a point charge or set of charges or a finite charge distribution. While this seems obvious, I cannot find a reason why this is true when inspecting ...
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93 views

What causes the electrical reaction between two carbon rods touching?

I recently watched this video in which carbon rods from a 6V lantern battery are removed and then touched together to create a makeshift arc reactor furnace. This produces electrified plasma which can ...
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27 views

Plotting the Graph of $1/I$ on the Y axis against R What does this represent? [duplicate]

What does the gradient, the intercepts represent, what is the equation of my line, and how do I use this information to calculate emf?
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89 views

Crazy? Generate unusable electricity

I know that sound crazy, but today I am wondering if there is a way to generate a current that is unusable by almost all electic/electronic devices? The idea would be to generate that current and ...
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2answers
34 views

Hydro-electric gravity problem - Is there a air-resistance-like force affecting water flow down a mountain making placing hydro-electric ?

Say I have a theoretical mountain with a river starting exactly at the peak. Gravity would act on the water, accelerating it down the mountain. There would also be a force limiting the water's ...
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28 views

Electromagnetic field to shield from EMP?

Could an electromagnetic field be use to protect against an EMP? As I understand, an EMP is an Electro Magnetic Pulse, so a sufficiently powerful field should be able to deflect one, right?
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75 views

Is lightning an example of energy emision from accelerated charge?

I have always heard that the inconsistency in explaining atomic models with classical mechanics was that the study of electrical charges had shown that whenever a charge is accelerated, it emits light ...
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32 views

Conductors and electric fields

I was given this problem: The maximum intensity of an electric field that can exist near the surface of a conductor in vacuum such that no field electron emission is produced is around $10^8$ V/m. ...
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2answers
42 views

Multimeter reading between wire & air

Why does a multimeter show 10-20 V(AC) when I connect one of its cables to the hot wire of a 220 V(AC) plug while the other cable is in the air? Also why does this not happen with a 5 V battery? (It ...
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38 views

where does electricity come from in piezoelectric?

I have some questions here. BaTiO3 is a material which exhibit piezoelectric effect when we give external pressure on it. It contain Ba2+, Ti4+, and O2- ion in its crystal unit. The Ti4+ ion will move ...
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1answer
44 views

Conductor held at constant potential

What does it mean for a conductor to be held at constant electric potential? So if my reference point is infinity, and I integrate inwards over the electric field to any point on the conductor, I will ...
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2answers
29 views

Finding the torque on a dipole affected by electric field

A $H_2$ molecule with charges $\pm p$ separated by $d=10^{-10}$m and masses $1.66\times 10^{-27}$kg is put into an electric field with uniform strength $E$, making an angle $\theta$ with this field. ...
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90 views

Why does my shirt make a crackling noise when it is static?

I thought that when clothing becomes "static" (used as a colloquial adjective for that state when clothing fresh out of the drier sticks to everything) it's because of a build up of electrons. That's ...
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1answer
57 views

How two electric charges know about each other? [duplicate]

Suppose we have two electric charges $q_1$ and $q_2$ a distance $r$ apart in euclidean three-space. Coulomb's force law states that there's a force $$\mathbf{F}_{12} = \dfrac{1}{4\pi\epsilon_0} ...
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84 views

Potential difference between Earth's surface and 2 meters above

Assuming Earth is a charged sphere of radius $R = 6400\times10^3$ m with uniform surface charge density $\sigma = -10^{-9}$ C/m2 and with $\epsilon_0 = 8.85\times10^{-12}$ F/m I find that ...
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35 views

Wireless energy flow through earths magnetic field

Seeing that technologies such as that developed by WItricity are based on magnetic fields, is it possible to transfer electricity that way through earths magnetic field?
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122 views

Show that the current in a cylindrical conductor is uniformly distributed across it's cross section

Using relevant equations for E and J, show that the current in a steady current I in a cylindrical conductor with uniform conductivity $\sigma$ is uniformly distributed across its cross-section. I ...
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37 views

Long life energy usage

Im doing a project on school. I want to re-use energy. I know that it will not run forever (but i hope it runs very long). So i wanted to ask if the image below is right and i could use it at school. ...
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25 views

Biological Signal Extraction Methods

EEG / MEG Back in 1929 Hans Berger recorded the first electrical potential variations in the brain from the scalp. Great advances have been made in this science since discover, with many scientists ...
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148 views

Electric field 0 everywhere inside Gaussian surface

Gauss's Law shows that the electric field everywhere inside a spherical shell of uniform charge density is $0$. Suppose we have a surface which divides space into two disjoint regions (an interior and ...
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40 views

How does the solar cell work?

As of i know that a solar cell consists of a transistor(NP) .First step it creates a barrier between the n type and the p type junction.Then following that the sunlight i.e,(the photons) supply ...
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53 views

Repulsion of electric charges

If a take a vacuum tube and put electrons in it and put a negative ion strip or something like that outside the tube will the electrons inside the tube start moving due to the repulsion of charges of ...
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251 views

Electricity is the movement of electrons or ions?

Electricity is the movement of electrons from one atom to another or the movement of charged negative particles (ions)?
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77 views

Understanding the relationship between electric energy and force

I'm trying to do the following problem: One of the three types of radioactive decay is "β decay", during which protons decay into neutrons or vice­versa, emitting either electrons (β­) or positrons ...
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88 views

Why can't I connection the anode of a battery to the cathode of an other battery and get a current flowing?

If I touch the anode of a battery or connect the anode the the cathode of an other battery, none (or rather: a very small current) flows between those two. If I instead connect the connect the anode ...
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2answers
248 views

Derivation of Faraday's law using Lorentz force?

For a stationary loop of wire with a time varying magnetic field $\vec{B}(t)$ through it. Is it possible to derive Faraday's law, using only the Lorentz force $$\vec{F}=q \vec v\times \vec B \tag ...
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37 views

current passing in primary circuit of transformer

When the secondary circuit is open ,why does the self induction found in primary coil would resist the flow of current in it? whereas in the small examples that I have taken in my studies from coils ...
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30 views

Non-linearity of energy conversion efficiency

I have a very general question to all of you. I am wondering if there is any basic physics principle that would state that energy conversion efficiency will be always non-linear (for the practical ...
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325 views

Which of the following has higher resistance - milliammeter or ammeter?

The question is the same as the heading - Which of the following has higher resistance - milliammeter or ammeter ? Now my teacher's and my answers don't match. It is assumed that the spring constant ...
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118 views

Static Electricity - Plastic comb, hair and small pieces of paper doesn't work for me?

All I have to do is run the plastic comb through my hair and hover it over small pieces of paper, right? The comb should then be charged and attract the pieces of paper... but that doesn't seem to ...
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92 views

Where do the electrons go?

In our house most of the plug-points have 2 holes. I know that one hole is neutral and other one supplies electricity. I can say that when i plug any device and turn the switch on electricity starts ...
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66 views

Static electricity experiment

My teacher always asks me to do the experiments on static electricity in winter. I don't know why? What will happen if I conduct the experiment in monsoon?
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84 views

What can happen when 2.3*10^28 positrons collide with 2.3*10^28 electrons? [closed]

I'm interested in this question after a writer friend asked me what happens when a human gets bombarded with positrons. Didn't want to post this under scifi because I want more "scientific" answers... ...
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1answer
62 views

Filament Lamp equation (Current/Voltage)

I'm starting to work with simple circuits (learning how to measure electromagnetic variables). I have been looking up on the internet for a formula or deduction of a formula that relates the current ...
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1answer
56 views

Can incandescent light bulb can be brighter if fixed power?

I found that luminous efficacy of 60 W tungsten incandescent bulb is 14.5 lm/W. Is this value defined by design details listed above or it depends on something else too? Can we design 60 W tungsten ...
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1answer
46 views

Why doesn't a levitating superconductor generate usable electricity?

Why doesn't a super cooled superconductor generate usable electricity due to the phenomenon of electromagnetic induction when placed upon a magnet? I basically mean, why can't it create electricity by ...
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95 views

Basic Conductor question

I have just taken a physics test in my high school in which one question posed that a positively charged rod is held near two uncharged spheres being held by silk filaments. Sphere 1 is held by a dry ...
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36 views

Why are trampolines more likely to give you a static shock when it is sunny?

It could just be in my head but I have noticed that I am more likely to get a static shock from my tramp when it is sunny than when it is not sunny. Is there a reason for this?
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110 views

Why is the potential difference across these two capacitors both 9V?

So above are two difference circuits, each with a 9V battery and a capacitor of the same capacitance. $C_1=C_2$ Why is the potential difference across both capacitors 9V? Shouldn't it be less than ...
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30 views

Potential difference on a curcuit

Above is a simple circuit. It has a voltage of 9V between the two terminals. I have drawn red lines which look like vectors, indicating how the current will flow. From the above diagram, I have a ...
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41 views

How would you define a difference in potential?

I'm currently in 12th grade, and am required to write an essay about physics and biology. The topic of the essay is the artificial brain (with the researches of the Human Brain Project in Switzerland ...
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219 views

Why do bowlers rub the ball before bowling in a cricket match

Why do bowlers rub the ball before bowling in a cricket match? What is the science behind it? Is it because of friction?
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112 views

Wait… why exactly does farady's ice pail experiment prove Gauss's law?

You'll notice there are no equations in this: that's because this is a question of morale, not of math. But a humble one at that! I come to learn, not to expound. But don't let that limit the form ...