# Tagged Questions

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

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### How is the direction of Magnetic/Electric Lines of Force Known?

It is shown that the direction of magnetic line is from north to the south and that of the electric line is from positive to negative. How do we/scientists know that the imaginary lines of force or ...
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### electric-circuits

Why can't you connect the + of a device to one battery and the - to another battery (and have it work)?
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### Wireless electricity through Wi-Fi power signal?

Could there be a method to obtain and send worldwide electricity through WiFi? I mean if we have internet everywhere and only need a WiFi device, can we apply the same to electricity technology? or ...
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### How do I calculate the speed of a temperature change?

I know how to calculate the change of temperature in a copper wire depending on voltage and current, but not how fast the temperature would change.
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### Power delivered by a plug

Ok so i know that (in the UK) the voltage of a mains supply is 230v. But when we plug a item e.g. a tv in to it what determines how much power is drawn from this supply. I presume it is the current ...
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### Understanding frequency of a signal

I'm trying to understand how can one transmit different signals on a same copper wire using different frequencies. How does the electrons actually interact with the frequency? And how does the ...
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### Why is electric current dangerous to humans? [closed]

How does a strong electric current harm our body? A strong electric current will posses a great charge. But how does that charge injure us?
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### Would it really require 44 car batteries to heat my pool? [closed]

After doing some research and math, I 'discovered' that it would take 44 (give or take 20%) car batteries to heat 1,000 gallon pool by 10 degrees. Is this right or am I missing something? It seems a ...
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### Do electrons move in a conductor when it is connected to only one pole of a power supply?

If I were to get a conductor e.g. a piece of copper wire or aluminium and connect it to one pole of a battery (let's take the positive pole for example), will electrons be removed from the conductor ...
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### Of all the electrical energy used in a home, is there any portion that won't eventually become thermal energy in the home?

Considering all of the appliances that the average home uses--microwaves, light bulbs, dishwashers, refrigerators--is it safe to say that all of the electrical energy in a home will be converted to ...
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### Is it possible to calculate the force exerted by two unequal charge, separately?

According to the Coulomb's law, when two equal like point charges are placed 1m from each other the force between them is 9 * 109. But if two unequal like point charges are placed, the bigger charge ...
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### How a plasma reacts with an AC electromagnet

Any metal conductor such as aluminium or copper is a conductor because of the free electrons in such metals. Plasma also has free electrons so I would like to know if you can repel plasma the same ...
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### Do high voltage power lines attract lightning strikes?

I always thought that high voltage power lines would attract a lightning strike more than other structures in the same area. Turns out I was wrong. My neighbor's chimney got struck by lightning and it ...
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### How does temperature affect an electrical current

Synopsis I have read an interesting article J. Halderman et al. "Lest we remember: cold boot attacks on encryption keys" in computer science regarding cold booting. The paper discusses how the use ...
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### Charge propagation in a long circuit

Imagine a long circuit that goes around the Earth, or just spans a large enough distance to measure the effect, say 100'000 km. The circuit has efficient light bulbs installed at each 10km mark. ...
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### Cause for Power Transmission Tower “Breathing”

OK, this question is not your usual one: Last night while hiking solo from the mountains back to my car at the mountain/desert interface (Lone Pine, CA), I had a rather bizarre -- and downright spooky ...
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### Why Change Of Magnetic Flux Induces Current In circuit?

Why change of magnetic flux with the time through a coil induces current in it? Please tell me that what happen to charge in the coil if the magnet or electromagnet wave around this? Also, why a ...
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### How is the current same on both the sides of a resistor?

I am wondering that how can current be equal on either side of a resistor as the work of a resistor is to resist the flow of electrons i.e. decrease the current. How is this possible?
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### Electric potential of spherical water droplet [closed]

I'm trying to answer the following: 1000 spherical water droplets, each of radius $r$ and each carrying a charge $q$, coalesce to form a single bigger spherical drop. If $v$ is the electric ...
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### Why are diodes able to amplify signals in groups, but not alone?

Single diodes can determine whether a signal passes or not (depending on the biased)(plus they can even rectify a signal), yet why does it take a combination of diodes(like a transistor) to amplify a ...
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### What exactly is three phase power? [closed]

What is three phase power? How does it differ from normal AC current?
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### Electric field generated by a point charge moving at the speed of light

As you see, this is the electric field generated by a point charge moving at constant speed v. I know that when $v$ -> 0, $E$ is just the Coloumb Law. But how do you interpret $E$ when $v$ -> $c$ ? ...
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### Why is emf equal to PD when circuit is “open”?

I understand that the set up of a battery consists of very good, but not ideal conductor, and therefore, some internal resistance exists. Also, I get that emf is the PD that would exist if the ...
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### Where can I learn the meaning of variables in a formula?

I am in a low level physics class that is taught in high school. We were given a couple formulas as seen on the board, but I don't know what the variables stand for (their names), and what units ...
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### If I charge a battery using a much higher current, can it explode?

If I have a 12V 4Ah lead acid battery and use a battery charger that, let's say for example, can charge 10A, 50A, or 100A. If I theoretically turned it to 100A will the battery explode? I understand ...
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### Alternative solar panels

I was doing a bit of thinking recently, when I stumbled on an interesting idea. In a simplified sense, solar cells function by absorbing light and converting it into electrical energy. Since visible ...
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### Boundary conditions of this problem

We have A point charge, a homogeneously charged insulator with total charge $Q''$ which is a ball with radius $R$, a conducting metal ball with charge $Q'$, radius $R$ and a grounded metal (no ...
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### In Leyden Jars, how does the outer metal get charged?

In a Leyden jar, I have read that a charged object is brought in contact with the conductor in contact with the metal inside the jar, thus giving the inner metal a similar charge. And the metal ...
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### Form factor and average value [closed]

Why Our Electricity Flowing in the Sequence of 11kv,33,66,132kv,why not Flow in 10 kv,11,12,13,14 that Sequence.
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### Potentiometer at null pointer!

Consider the situation when a cell of an unknown emf is being measured using a potentiometer. We slide the jockey so as to obtain the null point. Now, is there any current in the potentiometer wire at ...
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### Thermo-Emf variation with temperature

In the following experiment for seebeck effect After a certain temperature, the thermo-emf begins to fall. Why does this happen? What is happening microscopically at this level to cause such an ...
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### If we connect a source of electricity in a large water body ,will it be dangerous? [duplicate]

I was wondering whether a person will be electrocuted if he is in large pool or a sea which is connected through a source of electricity . As sea water is saline it will conduct electricity so will it ...
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### Why does rubbing feet against sheets create a spark?

Sometimes when I'm in bed at night, I rub my feet against the sheets and light is created. What exactly is going on? I'm familiar with static electricity, and the triboelectric effect (creating a ...
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### Charging a spherical capacitance

How could one charge a spherical capacitor with a battery or any other emf source?
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### How do substances with like charges repel each other?

I have read in a number of places how substances with opposite charges attract each other: The excess electrons in the one substance repels the electrons in the other substance so that they move away ...
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### What exactly is ''electric energy''?

If the two fundamental types of energy are kinetic and potential energy, is electric energy simply the kinetic energy of charge carriers? Also, is the statement "A cell converts chemical potential ...
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### Gas vs electric cooking

I've heard it said many times that you're more likely to burn food on an electric stove than a gas one, but I can't tell a difference. This seems to me to be a fallacy perpetuated by the natural gas ...
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### Back $emf$ and power?

The formula relating current to back emf is $V-E=IR$ where $V$ is the source pd and $E$ is the back Emf. Thus it can be seen that as the back emf increases the current decreases. But what is the ...
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### How is the wattage of electrical appliance specified?

What does it mean by a bulb is 60 Watt or 100 watt (I know it means it emits 60 or 100 Joules of energy per second, but at what conditions)? Which one glows brighter when connected in series?? What ...
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### What is the difference between S/cm and Scm-1?

Conductivity is noted in S.cm-1 in this http://pubs.acs.org/doi/abs/10.1021/ja502765n i wanted to compare it to the conductivity values listed on wikipedia for common materials. i could not find ...
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### Electricity and Dust

My question is, does an electrically charged material attract dust? Would it be possible to make a device like a vacuum cleaner based on a mechanism like this (in principle)?
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### Why and how will the string break?

While i was searching on the identity discussed earlier that is $$1 + 2 + 3 + 4 + 5 + ... = -\frac{1}{12}$$ I found a similar identity applied to physics concept. It started by arranging long ...
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### Static Electricity and Grounding Confusion

In an electroscope, you take metallic balls, and rub them with either a comb or a glass. Touching the balls with your finger is said to undo the effect of rubbing them with the comb or glass, since ...
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### Why can't an excess of electrons or holes by themselves cause current flow?

I am a beginner in electrical engineering. Often times (most cases actually), the underlying physics aren't really explained to us and we are just left to assume that it works "because it works." This ...
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### How might inducted current/ voltage in multiple coil layers connected in parallel behave?

This is a branch from this question. In the event that two or more layers are connected in parallel - would the energy created across each layer likely be significantly less? In the event of (say) ...
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### Other units of resistance [closed]

Resistance is $\frac{V}{I}$, and we get the unit $\Omega$. Another unit is $\frac{W}{A^2}$. How do you derive that unit?
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### Application of Displacement Current

I'm reasonably happy with the derivation and results of displacement current, however, I'd like to be aware of a few practical applications of this idea. So far, the only one I'm aware of is when ...
Why is the relative permittivity $\epsilon_r$ infinite for a conductor? Where does it come from mathematically and does it make physical sense?