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

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Can walking provide electrical energy?

This is more of a theoretical question, but is it possible to convert the energy you use to walk into electrical energy to say, power a light bulb?
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98 views

Defining electric potential energy

When we say that the electric potential energy at a point is X is that assuming we are using a positive test charge?
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75 views

How to get a function for the voltage across a capacitor connected to an AC voltage source? [closed]

I am looking for the way of obtaining a solution for $V_{c}$ ,as a function of $t$ depending of $\omega$, of the following differential equation related to an electrical circuit involving a low-pass ...
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1answer
242 views

How do capacitors work?

Say you have a battery, with a wire connecting the negative and positive terminal. Initially, (the transient state) the electric field is not uniform and is perpendicular to the surface of the cross ...
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4answers
186 views

Temperature and resistance?

Why does resistivity increase with temperature? The explanations I have heard so far are that increasing temperature increases vibrations in the lattice structure resulting in the number of ...
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102 views

Electric shock from a frayed wire

Let's say it's a laptop charger not connected to a laptop, and it is frayed near the tip. I am guessing about 20Volts runs through that area. Now if a person touches a bit of plastic below the frayed ...
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206 views

Electric field in wire's cross section?

 $\Delta V_{ABCDA} = - \int_A^A \vec{E} \dot{}d\vec{l}$ The requirement that the round-trip potential difference be zero means that $E_1$ and $E_2$ have to be equal. Therefore the electric ...
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1answer
248 views

The effect of high frequency AC current in a fresh corpse [closed]

Given two AC currents of the same intensity, eg 20 mA, but different frequency, 60 Hz and 20MHz, which one would be more likely to reach the heart ? I've read about the skin effect and how current ...
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2answers
50 views

Electric motors and change in flux

"When a current passes through an electric motor, the magnetic force on the motor causes a torque on the loop of wire causing it to turn". However, when the loop rotates, there should also be a ...
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4answers
326 views

Sign of Work and potential energy in electrostatics

Conceptual question: Suppose we have a configuration of point charges. If the potential of the energy of the system is negative, this means work is positive. I'm kind of rusty with my mechanics, ...
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76 views

Why Transmission of electrical energy without wires was not practical even after Tesla's proposal

Why we couldn't transmit Electricity wirelessly even after so many proposals available proposed by Tesla ? Tesla tried to generate more interest in Wardenclyffe by revealing its ability to ...
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1answer
60 views

Why does this automatic night light advertise money savings? [closed]

I just bought a night light to light the hallway since it receives no outside light. The one I bought advertises that it saves money because it turns on only during the night or (dark hours). I did ...
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1answer
121 views

The workings of the Hall effect?

I want to ask about the workings of the Hall effect. Why do the electrons come to rest on the edge of the wire? The magnetic field pushes them up, and the electric field pushes them forward. Shouldn't ...
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248 views

Surface charge in a wire?

The image above shows the distribution of the surface charge in a current carrying wire. The surface charges distributes themselves to make sure the field inside the wire is always perpendicular to ...
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467 views

Electric field in a wire?

The electric field in a wire is parallel to the wire's surface (it is always pointing "to the front"). If the electric field did not point in this direction, surface charges would build up and ...
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1answer
120 views

Superposition theorem

Is superposition theorem applicable for circuits having semiconductor components like diodes, transistors, etc.?
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144 views

Is it possible to use induction ampermeter to measure power consumption of electric water heater and dryer?

I hope this practical question is not OT and not too trivial for this forum. I am renting an apartment in a duplex with a shared water heater and dryer. Turns out, both water heater and the dryer are ...
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77 views

Why do some (older) wind generators have more than three blades?

Based on my personal observations, newer windmills seem to have three blades while older ones tend to have four or even more. This question has excellent discussion on my three is an optimal number. ...
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3answers
164 views

Why do batteries work?

Consider diagram A. In diagram A a car is at the top of a cliff. Gravity is pulling it down, but it does't move since its on a flat surface. Even though it would be at a lower potential at point B, ...
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1answer
88 views

Voltage in a circuit?

The voltage of the battery signifies the difference in voltage between the positive and negative terminal What does this mean? The definition of voltage difference I'm familiar with is the ...
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0answers
45 views

Is heat energy from electronics wasted in the winter? [duplicate]

In the winter, are not all electronics heating the house - thus no energy is wasted? Considering the energy I'm paying for: If I leave my computer running while I'm out, how much energy is actually ...
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3answers
373 views

Why does a faraday cage protect you from high currents?

In an electrostatic case it is clear that that in a space enclosed with a conductor (without charge in it) the electric field is zero. This is often demonstrated in physics shows like on the ...
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1answer
35 views

How do test lights (mains tester) work?

I was wondering how one-contact test lights work. Obviously there is a small current running from an energized pole through the human body somewhere that is still large enough to produce a visible ...
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0answers
45 views

Does all electrical insulator can be electrostatically charged?

Does all electrical insulator can be electrostatically charged, or insulator with only dielectric property can? Thank you.
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2answers
236 views

How do I combine three resistors which are in parallel with each other?

For this circuit (a and b are connected by a battery), Will I be able to find the total resistance of the circuit by adding resistors that are in series and combining resistors that are in ...
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1answer
89 views

Vortex shedding

So I was reading about vortex shedding, and got to know that it causes the building to resonate. Is there any way to use this resonance to generate electricity (maybe use quartz?) I am trying to make ...
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3answers
154 views

Electromagnetic Waves

We all know that light is an electro magnetic wave. but is electricity a EM wave? If it is then why light does not requires a medium to travel and why on the other side electricity needs a conductor ( ...
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3answers
595 views

Why does a fluorescent tube-lamp flicker before lighting up?

If you turn on a fluorescent tube-lamp, it flickers before lighting up. If you then turn it off and turn it back on after 2 seconds, this time it doesn't flicker but lights up straight away. If you ...
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2answers
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Solving circuits using kirchhoff's laws and elimination method ( not any matrix method) [closed]

I need to solve this problem as part of my review in college physics. The task is to find the value of 5 branch currents using Kirchhoff's laws and elimination method (or maybe called elimination by ...
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1answer
118 views

Some basic questions related to electricity [closed]

Note These questions may be incorrect. 1) Why do positive charges flow from high potential to lower, but the electrons do not? Am I wrong? 2) Does battery supply charge to a conductor? I read it ...
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0answers
47 views

What mechanisms require the use of different polarities in DC welding?

In gas metal arc welding, an electric arc forms between the work piece and a consumable wire, heating the work piece and also melting the tip of this consumable wire, which is continually fed into the ...
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1answer
85 views

How dangerous is a parallel plate capacitor which is used in physics demo experiments?

How dangerous may it be when experimenting with a parallel plate capacitor typically used in physics demonstration experiments? Take for example this one (that's what I use): ...
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1answer
41 views

Using a lemon's energy [closed]

Some simple exercises i need some confirmations on. Let's say a lemon has U = 1V and an average current of 0.1mA for about an hour. Q1. How much lemons do you need to light a 100W bulb. Is the ...
5
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1answer
143 views

Can I feel (the results of) electromagnetic induction from overhead rail lines in the human body?

A few weeks back, I was standing at a Hornsey rail station (in the UK) which uses overhead lines, and particularly has a number of parallel rail lines, all close to the platform. While I was standing ...
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2answers
69 views

how to model the exponential growth of luminosity when you flick a light on

My original thought was: $$ L = L_0 \left( 1 - e^{-t/\tau} \right) $$ where $L$ = luminosity and $L_0$ = initial luminosity. But when I tested this I found that the time constant $\tau$ was higher ...
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215 views

What is the maximum theoretical efficiency of heat to electricity conversion?

I know that heat engines (heat to kinetic) are limited by Carnot cycle and that kinetic energy to electric energy conversion via standard generator reaches over 90%. However I would like to know ...
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119 views

Questions about Van de Graaff generator

Only asking those questions because I can't afford to get a real generator. If the voltage on the sphere was 50 kV, then I used a metal rod to discharge it and I connected a voltmeter to wire ...
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1answer
167 views

Why touching tooth filling with aluminum foil feels so weird?

I have read that there is and electrical current, but why and how? How big can this current (and voltage) be (does an amount of foil, saliva, tooth filling have any influence on this)? Can it "dry ...
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1answer
87 views

What happens when the frequency of A.C becomes infinite?

In an alternating current, the flow of electric charge periodically reverses direction, and the number of times it does that is called the frequency of the current. However, if the frequency of an AC ...
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1answer
120 views

Shot noise at high frequencies (can it really be ideal white noise?)

Quantum shot noise (either optical intensity noise or electrical current noise) described by the noise spectral density of $2 e I$ (electrically) or $2 h \nu P$ (optically). So it is white noise. I ...
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2answers
138 views

Migration of an ion in a non-conductive medium

Someone asked me why, when performing DNA electrophoresis we need to put the gel inside a conducting buffer. Couldn't we just run it in distilled water? My answer was that if we had distilled water ...
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51 views

Does the presence of atoms hinder current flow?

When current flows through a material, electric resistance is observed when the electrons collide with the material's vibrating atoms. My textbook says that when we cool the material till the point ...
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3answers
202 views

Why is the field inside a hollow sphere zero?

Say you have a hollow sphere with a uniformly distributed charge on the surface. Why is the electric field everywhere inside the sphere zero? For the centre, its easy to add the vectors from the ...
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3answers
143 views

electron flow in capacitor with dielectric

if I make a circuit with a battery and a capacitor (with a dielectric inside), how it is possible to get a current in the circuit? If electrons go from one pole of the battery and they arrive to one ...
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1answer
42 views

Capacitance of a free conductor

Consider a ideal conductor in free space.For all purposes here,the zero of the potential is taken at infinity. Suppose I give a charge $Q$ to the conductor.As a result,the conductor will have a ...
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5answers
216 views

Why is electric potential 0 in this case?

On a test, we had a question where there are 4 point charges at the vertices of a square. The 2 charges at the upper vertices have charges of +q and the 2 charges ...
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0answers
40 views

Capacitance in a capacitor

This here is a question that I just don't know what to do with. I don't know what I'm doing wrong. "A plate capacitor consists of two plates with area 2.5 cm$^2$ at a distance of 1.6 mm from each ...
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2answers
231 views

Will I get a shock when I try to use my hair-dryer under water?

Occasionally people get killed in their bathtubs by having an electrical device such as a hair-dryer take the bath with them - in movies. It seems to be a common belief that this is realistic, even ...
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1answer
71 views

How magnets create electricity in conductors?

what are the reasons for current appearing in a wire when wire is in a changing magnetic field?
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1answer
122 views

In a positively biased PN junction, where do the injection carriers come from?

I am not quite understand i-v character of PN-junction diode. Here is the model in textbook. The PN junction diode can be divided into three regions. They are One depletion region near the PN ...