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

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Capacitor charge and current as a function of type question [on hold]

Two capacitors, one resistor and an ideal battery are connected through switches s1,s2 and s3 as shown in figure. Initially capacitor of capacitance 4C is charged, while other is uncharged. The upper ...
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1answer
24 views

Resistance of a general resistor

I have some medium with a resistivity which depends on position. In this material are two electrodes, is there an integral or something which i could numerically integrate to find the resistance ...
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1answer
17 views

If we increase dimensions of a wire, how does electron density change?

If we increase the diameter of a wire, does the electron density change at all? When we increase the diameter or the length of a wire (while solving numericals) do we add appropriate number of ...
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1answer
25 views

I need proof for dW=eIdt [on hold]

I need help to understand from where this equation is formed inorder to continue to study energy stored in an inductor.
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1answer
35 views

If increasing applying energy to an atom excites electrons, why does electrical conductivity decrease as temperature increases?

Applying energy to an atom makes the electrons jump up to higher energy levels. This is known as excitation. Electrons on higher energy levels are easier to remove from an atom than those on lower ...
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1answer
60 views

Why doesn't a fluorescent lamp implode even though the pressure difference is very high?

According to Wikipedia, the pressure inside a fluorescent lamp is 0.3% of the atmospheric pressure, so the pressure difference between the outside and the inside of the lamp is almost equal to the ...
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1answer
11 views

Arc reduction on curved electrical contact [on hold]

Why does is arcing reduced by establishing a radius(curvature) at the sides of a relay contact?
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2answers
49 views

Does temperature have any effect on static electricity?

This is one of those questions that came up during a discussion with a friend on static electricity. His argument (which I dispute) is that there must be a relation between temperature and the ...
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1answer
39 views

What happens when the switch in this circuit is flipped? [closed]

what would happen to lights A and B if the switch in this circuit is flipped?
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15 views

How to apply kirchoff's laws to motors in DC and AC settings

DC case: is it ok to treat a motor as a variable resistor, with resistance depending on the load? AC case: suppose I have a motor that runs at 120V AC and is rated to X watts, how can I determine how ...
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30 views

how come if you rub polythene with wool it gains electrons, but if you rub perspex with wool it loses electrons? [closed]

what makes a substance gain or lose electrons when it is rubbed with wool?
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2answers
42 views

Some questions related to circuits and flow of electrons

I have some doubts related to electric fields and flow of current. So, let us assume an electric circuit, which contains a battery and a wire connecting positive and negative terminal of the battery. ...
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1answer
32 views

Why are there no charges inside a conducting sphere?

Why is it necessarily true that all charges occupy themselves only on the surface of a conducting sphere, and not anywhere inside the sphere? One argument is that if a charge were to be inside a ...
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Does potential difference or electric field change with distance between parallel plates?

Say you have a set of parallel plates, one is positive and one is negative, if you change the distance between them would electric field strength change or potential difference, given the equation ...
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0answers
37 views

How do I find the equivalent resistance of this resistor network? [closed]

I was trying to find the resistance of this network of resistors Until I got stuck at this So, how do I go about from here? Any help would be appreciated. There's just one catch, you are not ...
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0answers
23 views

Efficiency of resonant inductive coupling as a function of distance

What is the relationship between the efficiency of energy transfer between resonant inductive coupling between two coils, and the distance between the coils?
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36 views

How to increase Resistance of a conductive material?

I'm working on a project that I should measure the resistance of conductive sample ( like brass ). But I've a problem. Resistance of conductive samples is too low which requires a miliohm meter to ...
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2answers
43 views

What is meant by “current” in this context?

This is a quote from Optics by Hecht: A stationary charge has a constant E-field, no B-field, and hence produces no radiation—where would the energy come from if it did? A uniformly moving ...
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2answers
27 views

Confused about two formulas for electric field magnitudes

So I am going through my notes and I come across these two equations which both describe electric field magnitudes (I think.) $$\frac{k q}{r^2}$$ and $$\frac{Q}{A \epsilon_0}$$ Could someone ...
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0answers
11 views

Force on a magnetic dipole due to a magnetic field

Imagine a solenoid which has current $i$ and is producing a magnetic field $B$ which equals $$B=\mu N i$$ Now, imagine we put a small cylindrical magnet at the end of the solenoid. Then because at ...
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20 views

Force Exerting on a magnetic train

A question is already asked ( How does this “simple” electric train work? ). But I've got a question about it. In order to calculate the force which is being exerted on the system including magnets ...
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0answers
20 views

How do electrons choose their way through nodes? [duplicate]

Suppose I have a circuit, powered by some emf ($V$). If I put two resistors $R1$ and $R2$ of different resistances in parallel, the current at the node is divided following Kirchhoff's circuit laws. ...
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0answers
21 views

Van der pauw method for an isolated hole

Van der pauw method is a way to measure the resistivity of a material with arbitrary shape while it meets some specifications ( being homogeneous and ...). One of the conditions is that the sample ...
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1answer
22 views

Do we need wires for current conduction in ionosphere?

As we all know in ionosphere there are free ions and electrons present. So if we somehow take a bulb and a battery in the ionosphere then will the bulb glow due to conducting nature of environment ...
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4answers
54 views

Electrons flowing through a circuit make it warm, where does that heat come from

in a circuit I have a low resistance device that consumes many watts, in normal operation this device will get warm; where does this heat come from? the law of conservation of energy states that the ...
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26 views

How to figure out if an element in a circuit is absorbing or delivering power?

. Eg: In the above circuit. 50v source and 0.2Va current source is said to absorb power.If power is absorbed,what work is done with the absorbed power.
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90 views

Which scientist is this?

Okay so I was watching discovery channel, in that i saw a man cleaning live electric wires of 10k volts in the air, he was not touching the ground. They said he was able to do this because of the ...
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2answers
97 views

Charging by induction [on hold]

When we charge an conductor by induction and grounding, we first bring a negative charge to the conductor. As a result the mobile electrons of the conductor get repelled and stay far from the negative ...
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32 views

Ambiguous phenomenon of CFLs [closed]

During night when I close my all lights, few CFLs at my house flash periodically with different time periods. For example: one at my room glows after every 1 min 5sec . It is of 42 W. I= 300 MA. It ...
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2answers
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Electrical injuries - Doorknob vs powerline

This is something that has bothered me since high school physics. I have a medical and engineering degree, yet I can't for my life answer this question in a way that's logically consistent in my ...
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0answers
28 views

What do we mean by live and neutral wire? [duplicate]

In our household circuit we have ac supply of 50 Hz. It means current reverse its direction in every 100th second. I think then, current flows in one direction then another.Then, why do we have live ...
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1answer
37 views

electric field's area [closed]

How much area an electric field surrounds? since we're just able to draw the electric lines of force we sometimes think that the field is though 3d but surrounds a finite area.But is it measurable or ...
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3answers
78 views

What changes in the electrons before and after a voltage drop?

It is easy to visualize gravitational potential energy as a function of the position of height, and a change in this potential is manifested in a change in height. Further, by the work-energy theorem ...
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0answers
18 views

The frequency induced by the alternating current

Let set up the experiment as followed. A string is stretched at two ends. Two magnet poles N and S are placed under and above the string. Now we let an alternating current go through the string with ...
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1answer
40 views

Electric field along a wire and load

I have referred to many books and all of them apply loss in potential across a resistor only in case of circuits. However, the electric field is present in the whole conductor. Hence the electrons ...
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22 views

Why does the metal mesh in an electric swatter make a whirring sound?

I have an electric bug swatter that operates on a rechargeable lead acid battery. I had one before that operated on disposable batteries and when it was turned on, it made a high pitched whining ...
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1answer
30 views

Physics Static Electricity [duplicate]

If a person has plastic soles, and are playing on Artificial grass and then the person touches metal goal post, the person will get a static shock.. Why?
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1answer
29 views

What will be the effect on coulomb force if any conductor is placed between the electric charges?

I know that if any insulator or dielectric is placed between the electric charges then coulomb force decreases by factor known as dielectric constant.So, what will the effect when any conductor is ...
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1answer
42 views

Experiment: releasing the copper bar above a permanent magnet

A classic experiment shows that when we drop a magnet through a copper coil long tube, there is eddy current induced in the coil. Then, due to lenz law, the motion of the magnet will be opposed and it ...
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1answer
47 views

How exactly does a bulb light up?

A typical value for the electron drift velocity in a copper wire is $10^3\ \mathrm{m\ s^{-1}}$. In the circuit below, the length of the copper wire joining the negative terminal of the batter to ...
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37 views

Lightning sprites

Lightning usually occurs due to an electrostatic discharge between an electrically-charged cloud and the Earth's surface, or between clouds. There are also sprites, electrical discharges that occur ...
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5answers
509 views

What is electric energy since electrons are not consumed?

I am interested in electronics as a hobby, so I have been reading up on the physics of electricity. I understand that difference in charge on battery terminals causes electrons to flow naturally ...
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2answers
36 views

which is efficient on solar electricity by photo voltaic or thermal

As we know solar energy used to generate electricity in two major ways: photovoltaic and thermal energy. The most small applications or personal use are mostly using solar cells. But when it comes to ...
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0answers
25 views

Calculating torque needed to climb a graded hill [closed]

this is my first post but I'll try to give my best understanding of the problem. I've been designing an electric skateboard which is driven by only one of the rear wheels (for the moment). As I was ...
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1answer
33 views

Why is current shared in a parallel circuit but not a series circuit?

Electricity test coming up. It's not clear to me why current is shared in a parallel circuit but not a series circuit.
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2answers
33 views

Can a floor made of copper pennies produce a static electric shock?

A friend is going to install thousands of pennies in a mosaic layout to be used as flooring in his home. Can this floor produce a static electric shock when walking on it? Is it possible to ...
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1answer
71 views

Why don't you get electrocuted when you jump and touch an electric fence?

I've read that you won't get electrocuted if you jump and touch an electric fence because you aren't closing the circuit with the ground. Which is also why birds don't get electrocuted when they're ...
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2answers
63 views

Will spinning DC motor in space generate infinite energy?

If I take a DC motor far in space and spin it, will it continue to spin forever and generate infinite electrical energy? If so, then won't it violate law of conservation of energy?
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1answer
36 views

Is the electric field in the wires of the parallel circuit always the same and how that affects current?

When we connect two resistors connected in parallel with a battery, it creates an electric field through this wire. well, my question here: Is the electric field in the main wire is the same as the ...
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1answer
69 views

Why does an electron lose all of its energy in a resistor?

Why does the electron uses nearly all of its energy for one resistor in a simple circuit made of a battery, wire, and resistor? I really need to know what happens exactly at the atomic level in the ...