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

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Different batteries connected in parallel

If we have 2 batteries one of emf x and the other is of emf y and we connect them in series we get an effective emf of x+y. But what if we connect them in parallel, how to calculate the emf now?
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482 views

Do black holes have charges?

Do black holes have charges? If so, how would they be measured? Also, does electricity behave the same way? Black holes affect photons, which are carriers of EM radiation, so do black holes have any ...
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2answers
321 views

Simple ohms law on a battery ? Paradox or conceptual error?

Suppose we have a regular pencil battery which supplies DC voltage $V$. Say we take copper wire and connect the ends of the battery to an $R$ ohms resistance. Then Ohm's law tells use the current in ...
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14k views

Why don't electric workers get electrocuted when only touching one wire? [duplicate]

I know that when electricians work on the poles on the streets, if they only touch one wire at a time they will be fine. However, from my understanding, the negative wire is connected to a large ...
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5answers
10k views

Why does the comb attract the pieces of papers if they're neutral?

When we rub our hairs with a comb, and then try to attract small pieces of paper, they're attracted by the comb. The pieces of the paper were not electrified before they were attracted. Then they ...
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58 views

Early Concepts in Relation with the Forces Produced When Certain Pairs of Objects are Rubbed Together

It was found centuries ago that these materials: wool cloth and paraffin wax, glass rod and silk cloth when rubbed against each other attracted one another. While two glass rods when rubbed against ...
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1k views

What types of materials can be electrically charged by rubbing?

What types of materials can be electrically charged by rubbing? Is there a certain type of materials in which static electricity can be produced by rubbing together two different materials?
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4answers
4k views

Capacitor Charging and Discharging when connected to the ground

When we charge a capacitor using a battery and then remove the battery, the plates of capacitor becomes charged. One holds positive charge and the other one gets equal negative charge. o. k. ? Now ...
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11k views

Definition of electric charge and proper explanation

Is there a definition of electric charge and proper explanation of it? It is said "Electric charge is the physical property of matter that causes it to experience a force when close to other ...
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1k views

Charging Glass Rods

When we rub two glass rods with their respective pieces of silk cloth, the two glass rods would repel each other. What if we rub the glass rod against the other glass rod? Will they repel each other? ...
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2k views

Definition of Static Electricity

The result of an imbalance of electrons between objects is called static electricity. It is called "static" because the displaced electrons tend to remain stationary after being moved from one ...
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63 views

Capacitors discharging in series [duplicate]

If you connect positive plate of a charged capacitor to ground, it doesn't get discharged. Now consider $4$ capacitors of equal capacitance connected in series to a $10\, \mathrm{V}$ battery. Connect ...
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5answers
700 views

Relativistic charge density in a closed loop

When charges of conductance are at rest, there is an average distance between them. The relativistic origin of magnetic field says that distances between electrons shrink when they are set into a ...
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2answers
517 views

Electric shock from a power line [duplicate]

A bird perches on a bare high power line and nothing happens to it. A man standing on ground touches the same line and gets a fatal shock. why?
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5answers
5k views

How can Ohm's law be correct if superconductors have 0 resistivity

Ohm's law states that the relationship between current ( I ) voltage ( V ) and resistance ( R ) is $$I = \frac{V}{R}$$ However superconductors cause the resistance of a material to go to zero, and ...
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3answers
168 views

Voltage of open circuit

A battery with emf $\varepsilon$ and internal resistance $r$ is connected with a resistor $R$ in the following open circuit. What is the voltage $V_{ab}=V_a-V_b$? The answer is $- ...
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1answer
611 views

Is it possible create current by spinning a charged sphere?

If we have a sphere which has $σ$ surface charge density and rotate it in axis z will this create current ? Is it possible without any potential difference ?
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2answers
3k views

Light bulbs, Wattage meaning? [closed]

Light bulbs, Wattage meaning? Two incandescent bulbs (120 V, 25 Watt) and (120 V, 500 Watt) connected to the same batteries. Which one shines brighter? And why?
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1answer
340 views

Joule heating due to the (slow) electron drift velocity?

I understand the concept of why the signal speed is higher than the electron drift velocity, but I can't understand the concept of joule heating. If electrons move slow then how do they produce a lot ...
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1answer
680 views

Why do aqueous solutions always “have to be” electrically neutral?

I was reviewing some analytical chemistry and stumbled upon a section that explained the imperfection of using a salt bridge. It said that the using dissimilar ions is a problem because in, for ...
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1answer
2k views

The electric field of a conductive sphere containing a charge - grounded vs not grounded

Let's suppose we have a sphere but unlike theoretical ones it'll have some thickness say $\Delta r$ and inner radius $R$. What I was wondering about is how will it behave if we place some charge $q$ ...
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0answers
79 views

Current between supeconducting rings

How to calculate the current between two superconducting rings with radius r separated by a distance d? Please note that being unfamiliar to the concept of superconducting rings, I can't approach ...
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3answers
2k views

How electricity, and generating electricity works on the atomic level?

I am trying to understand the basics physics as to how electricity works. Unfortunately it seems most online material is either complex full blown mathematical equations, or water pump analogies. I ...
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3answers
415 views

Producing electricity from all wavelengths of electromagnetic spectrum

Is it possible to produce electricity from all wavelengths of electromagnetic spectrum beside visible light ?Like using gamma rays or x-rays .
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Is there any example where electric and magnetic fields are not perpendicular?

Perpendicular electric and magnetic field creates light or other electromagnetic waves. Is it a necessary property to have a perpendicular fields? If not what would happen when the fields are not ...
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7answers
8k views

Why is the charge transferred by electrons and not by protons?

Charges are transferred by electrons which we all know. But why can't it be transferred by protons? Well, I searched on Google where I found similar questions already being asked on many sites. ...
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46 views

Nature of electricity [duplicate]

Suppose a lightning strikes and there is an iron rod and a coconut tree. How does the electricity know that rod is the least resistant path before hand.
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1answer
3k views

AC passed to a DC motor

What would happen when an alternating current (AC) is passed to a DC motor? And a direct current (DC) passed to an AC motor? Will it work or not? What will happen to it?
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2answers
155 views

Static discharge out of 3 volts button battery

I am starting to get interested in static electricity I have found this which is very cool but I do not know how I can control the output voltage. ...
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184 views

Why isn't this capacitor charging?

Let's say you have a parallel plate capacitor and you connect one plate to the positive terminal of a battery and the other plate to the negative end. So this is like a static situation, you have a ...
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4answers
1k views

Why there is no “Edison” unit in physics? [closed]

In the popular culture the XIX-XX century competition between Thomas Edison and Nikola Tesla is well-known. The example could be the Prestige movie, where there are some "Edison's agents" who sabotage ...
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1answer
968 views

How much of current flows through a bird sitting on a power line?

I've been googling for hours and went through over a hundred answers. Now, some say the bird doesn't form a closed loop, some say the current is so small that it doesn't kill the bird. From as much as ...
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2answers
7k views

How does current flow from the emitter, through the base and to the collector in a NPN transistor?

So, I understand that for a NPN transistor to work the emitter-base junction needs to be forward biased and the collector-base junction needs to be reverse biased. I understand how current flows from ...
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1answer
92 views

Can someone explain this intuitively please?

In a static situation we defined voltage as energy/unit charge, or j/c. As the distance between the charged particles increased, the voltage decreased. Now why do we not apply this in a simple DC ...
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1answer
82 views

Is there a material that changes local conductivity

I hope this is the right forum to ask this question. Is there a material (preferably thin, like a membrane) that changes its local conductivity (by that I mean the permeability for an electric field; ...
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1answer
3k views

How electrons act under rotating magnetic field?

I study Power Engineering in University. Today I asked my lecturer to explain me exactly how atom's electrons act under spinning rotor's magnetic field, that generated dynamic electricity. But he even ...
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1answer
77 views

Reducing deposition on power supply wires

From my house there are two wires, i.e. a live and a ground wire which are placed on the power supply lines by a hook. They are not tightly jointed because of some reasons. These two wires are also in ...
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2answers
266 views

If we connect a block of p-type semiconductor only to a positive terminal, will it become positively charged?

Connect the positive terminal of a battery to a piece of p-doped semiconductor, say, silicon doped with boron. Will the terminal pull electrons out of the doped silicon, or equivalently, inject holes ...
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1answer
114 views

What happens when a compact fluorescent lamp implodes?

When a incandescent lamp implodes, the filament burns up and the current is interrupted. Yesterday, a compact fluorescent lamp imploded and blew all the switches / fuses. I'm not sure if the same ...
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5answers
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Why is AC more “dangerous” than DC?

After going through several forums, I became more confused whether it is DC or AC that is more dangerous. In my text book, it is written that the peak value of AC is greater than that of DC, which is ...
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1answer
121 views

Thermal conductivity affected by electrical current

Does anyone know of any materials whereby the thermal conductivity can be changed by passing an electrical current through the material?
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1answer
845 views

Does the electric field inside a sphere change if point charge isn't in center?

As i understood , if you have a point charge in the center of a hollow conducting sphere then the electric field inside it, is zero because the charge distribution is spherically symmetric. But ...
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2answers
2k views

Is it possible to get energy from electrical wire using induction?

Pardon me if this is a stupid question but my physics courses are from a long long time ago and I was a teenager back then. ;) Electricity in a wire generates electromagnetism, right? Would it be ...
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3answers
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Calculating engine starter’s energy use

During a discussion on start-and-stop vehicle technology some bloke began pushing the point that re-starting the car uses stored energy from the battery, which needs to be replenished by increased ...
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3answers
6k views

How exactly does a resistance reduce current?

I've heard that resistors are used to decrease current to a particular appliance, such as in the regulator of a fan. However, I've also heard that the total current in a circuit is always the same- in ...
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0answers
46 views

pressure required for displacing a single electron off a crystal

I need to know this for my project- "power generation using the pressure applied on a keypad of a mobile electronic device". How much pressure does it take to displace a single electron off its ...
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2answers
7k views

What causes fluorescent light bulb to light up when it is near a plasma globe? Can this phenomenon be used to generate electricity in a circuit?

When a fluorescent light bulb is placed near a plasma globe, despite the fact there isn't a closed circuit, a part of the light blulb would light up. I tried measuring the voltage of the air ...
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2answers
196 views

What happens to this potential energy?

Let's say I turn on a Van de Graaff which creates a large positive charge. Now let's say I have an object with a positive charge in my hand and I start walking toward the Van de Graaff from $x$ meters ...
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1answer
161 views

Am I properly identifying the resistor terminal voltage?

The frequency applied to a circuit of voltage 120 V with a real coil and a resistor has a value of 50 Hz. The resistance of the resistor is 10 $\Omega$. The voltage at the resistor terminals ...
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1answer
82 views

Microscopic fields inside a conductor

In a neutral conductor if we assume electrons as point charges, the electric field in the space between them cannot be identically zero. This microscopic field may be very weak. What if we were very ...