Questions tagged [electricity]

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

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52 views

Electron gun design

I have a question about electron guns. I have read a lot, and all designs use high NEGATIVE voltage ($-1000$ V for example). Is possible to use high POSITIVE voltage like this drawing? Or do you think ...
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electric force of rubbing [duplicate]

When rubbing a ruler with my hair and get it closer to some pieces of papers , it'll attract them (they'll effect each other by an electric force). But why ? WhenI only charge the ruler not both of ...
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What happens when we use Faraday induction on a coil that already carries a current?

Consider the following experiment: (1) Attach a coil to a current meter, and run a magnet over that coil, measuring the current generated. This is ordinary Faraday induction. (2) (i) Attach the coil ...
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How does the thickness of a sample affect the accuracy of four-point probe resistance measurements?

I have been reading up on my experimental techniques, and I found a description of four terminal sensing here. It makes the statement that for accurate measurement of resistance the thickness of the ...
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How to use energy conservation in following case [duplicate]

A capacitor of capacitance C is intially uncharged is connected with a battery of emf ε.Find the heat dissipated in the circuit during charging?How can we apply energy conservation although there are ...
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Only getting positive values for induced voltage? [closed]

We have to draw a voltage over time graph for the induced voltage in a coil for 2 whole turns. $N = 10$ $B = 30mT$ $A = 100cm^2$ The coil is rotating at 20Hz We have the formula: $2πNBAfsin(2πfT)$ ...
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Does current flow in the wire when only one terminal of the battery is earthed?

Let me specify beforehand that this question has been asked previously but I haven't been able to satisfy my curiosity.I know a battery maintains a potential difference between it's terminals , let's ...
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I inserted my DC toy motor into and AC power outlet. Sparking happened and the motor isn't working anymore. What exactly happened?

What took place inside the motor and why isn't it working anymore? I familiar with basic electricity and circuits, but can somebody explain it in easy language.
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Confusion about electron flow and current

So, I learned in class that current is defined as positive charges moving from south to north. However, in all reality, the negative charges are moving, but the convention of positive to negative wors ...
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1answer
37 views

Overestimation Problem [duplicate]

I had asked this problem earlier but I was too vague in how I asked it so I'm making a new post to be more specific. Problem: Say we have a series circuit with an ammeter, a cell with internal ...
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How can the Neutral wire be 0V if its AC? [duplicate]

So I understand Alternating current like a battery, in which the Poles are constantly changed out, so the circuit stays completed, but the electrons change directions. But how can then in an AC plug ...
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When the external resistor increases in temperature, why is the calculated value for internal resistance higher?

Say we had a circuit with a cell (with internal resistance)and an external resistor of 10 ohms as shown: The 10 ohm resistor then increases in temperature, leading to an increase in resistance in ...
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Robert Boyle's discovery of electricity

I want to know what is the contribution of Robert Boyle in this discovery of electricity after Otto von gueriche?
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Does Kirchhoff's rule break down as it applies to capacitors

A homework problem asked me to find the voltage across a series of capacitors after they came to equilibrium. Essentially a capacitor C1 with a capacitance of 6.0 F is charged until the potential ...
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Lightning in space, would it be a perfectly straight line?

I have read this question: Can lightning happen in a vacuum? I do understand that here on Earth lightning consists of electrons moving in space and some of these electrons are tracing path, and ...
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1answer
31 views

What is the most energy efficient source of electrons?

Wanting to build a cathode ray tube, and I see there are a few electron sources such as thermionic emission and field electron emission. Since my project is small scale, since I don't want to go to ...
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Is it possible to create and control a magnetic field in a dielectric material?

A capacitor is usually formed by an insulater between two conductive plates. By applying voltage difference between the plates we create an electric field within the insulator in one direction. If you ...
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114 views

Evaporating tungsten wire

Consider an incandescent bulb having a thin filament of tungsten that is heated to high temperature by passing an electric current. The hot filament emits black-body radiation. The filament is ...
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Why aren't electrical power generators housed in “floating” structures that would allow them to spin?

Every generator I've ever seen is housed in a fixed mount, and uses a rotating magnet in a column, powered by something like combustion, or wind, to generate a current through Faraday induction. But ...
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What is the cause of resistance?

I searched for this question on the internet but didn't got a satisfactory explanation. What I thought on the topic is that the cause of resistance is 'the effective nuclear charge'. The nucleus ...
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51 views

Why isn;t the electric field at all points within concentric metal spheres zero? [closed]

Consider the question: A solid metal sphere of radius a, carrying a charge of +q, is placed inside and concentric with a neutral hollow metal sphere of inner radius b and outer radius c. Determine ...
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Electric Field and Electrostatics

Is centre of charge possible in Electrostatics? or is it just a method to reduce calculation Complications(under specified terms and conditions)?
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1answer
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I got this formula but can anyone prove it [closed]

Yesterday while doing some questions, I came across a formula that if a wire with uniform resistance R is made into n sided regular polygon then the net resistance between any two corners with $x-1$ ...
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1answer
66 views

Why does a voltaic cell induce an electric force proportional to voltage?

I'm trying to understand the intuition behind Ohm's law (that current is proportional to voltage). I understand the basics of the Drude model: if the electrons frequently collide and on average reset ...
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33 views

What is the density of air inside an electric arc?

It seems to me that at least after (but I would guess it happens also just before) ionized air allows conduction of a current, there is an elevated mechanical tension along the molecules forming the ...
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Parallel circuits at home

My textbook states that if you have a light bulb turned on and you connected a hair dryer with it in parallel, then the brightness of the light bulb will decrease. The reason my textbook provided, ...
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81 views

Why I can't find a value for the resistivity of plastic? [closed]

I'm working to a relation about resistence of various materials. I haven't found a table of resistivity wich includes Plastic. Is searching plastic too general? Does a table in which there is at least ...
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1answer
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Timing of lights switching off when the power source is disconnected

Not that I don't know the norms, but I have a doubt. Say, in the middle of a very large and well-lit city, is the power station powering all of the lights. If I were to view from space (or at least ...
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Unit conversion between dynes and newtons

I am learning Electricity and Magnetism by myself. Can someone explain me the math behind the equation below? (Quoted from Edward Purcell's Electricity and Magnetism (Cambridge University Press, ...
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135 views

Why doesn't electric field of an electromagnetic wave cause an electric shock?

An electromagnetic wave can have an electric field magnitude of more than 1000 V/m, which is a very high potential difference. When the light shines on you, why don't you feel an electric shock?
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What is the Electron Flow in a wire with 2 power sources 180 out of phase?

If you took two independent power supplies and set them to a sine with each power 180 degrees out of phase. The powers supplies will share a common line and the load will be equal_____________? Do ...
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My fingers are sparking large source of electricity when I touch plastic boards covered with polythene

Still I don't understand why am getting such voltage & it's the same feel that I touched 250 voltage of current. Also when I put two fingers on opposite direction (when I am removing polythene ...
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Derive electrical power from electrical work

I am a little confused with some aspects of electrical power and electrical work. The example is connected to a thermodynamic problem: Consider an adiabatic vessel filled with an arbitrary fluid. ...
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Direction of the current and the electrons [duplicate]

If the electric current is defined as Coulomb/second, why is the direction of the current is just the opposite of the direction of the flow of electrons?
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What should be the independent variable in a resistance experiment?

I was asked a question by a student today and I have been pondering about it for a while now. In an experiment to measure resistance of a conductor, should we vary voltage across the conductor and ...
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127 views

Electric dipole and collisions

An electric dipole consists of 2 oppositely charged particles (having the same magnitude) separated over a small distance. Now if opposite charges attract each other then wouldn't 2 charges making a ...
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2answers
66 views

Finding electric potential via direction of EMF

I was trying to solve this question: I understand that if the current is increasing leftward, then via Lenz's Law, the direction of the induced EMF will be to the right. Given that I now know the ...
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Why is a net flow of positive charge in one direction equivalent to a net flow of negative charge in the opposite direction?

If I understand correctly, conventional current was defined with reference to positive charges because it was found that a negative charge flowing in one direction is actually equivalent to the same ...
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Difference of Electric Potential between to points in an uniform E-field

This is an exercise to calculate the difference in potential between two points $A$ and $B$ in an uniform $\vec{E}$ electric field. It goes like $V_{B} - V_{A} = -\int_{A}^{B} \vec{E} \cdot d \vec{s}...
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Exponential fit in Origin doesn't converge

I am using a data treatment program called Origin, wich I think many of you are familiar with. The data I have is time vs voltage in the resistor of an RL circuit. The expression that describes the ...
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How can a capacitor restrict current to a load in a simple AC series circuit?

I've been scratching my head at this all afternoon. I understand how a capacitor behaves in an AC circuit and I understand how to calculate reactance, but the problem I'm trying to solve is how to ...
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Why electricity does not seem to alter metal mirrors reflection? [closed]

If individual electrons absorb and reflect photons, and if those electrons happen to be on a conduction band which is most probable as the outer electrons have a greater probability of intercepting ...
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Kinetic energy and current

When a battery is connected to a resistance circuit, we know that it loses energy because heat is emitted as a result of the collisions between the electrons and stuff, but my question is, is the ...
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Reactionless propulsion theory. Will resistance to the flow of electricity within a moving conductor result in a propelling force?

I believe that a conductor which is physically moving in the opposite direction to the flow of electricity will result in the motion of the conductor being resisted and this resistance will cause the ...
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Electric current in a circuit with two batteries [closed]

I have the following circuit                             &...
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Transformer Equation Confusion

I have read some posts on here which I think to revolve around my problem too but couldn't really understand the explanations. So basically, I have seen how the Transformer equation is derived: $\...
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1answer
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Direction of magnetic field around a straight current carrying wire

I am currently studying for O Level and I have been learning about electromagnetism for the past year. The topic has never clicked for me because I've never been taught the true relationship between ...
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1answer
186 views

EMF generated by a rotating rod can be zero?

I have taken a look at this question: Emf generated by a rotating rod But my question is different: A metallic rod is being rotated in a uniform magnetic field with a constant angular velocity $\...
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526 views

What do we mean by positive terminal and negative terminal?

What do we mean by positive terminal and negative terminal of battery ? What is the electric potential of both positive terminal and negative terminal ? Does positive terminal mean positive electric ...
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Can you generate 3-phase AC power from linear motion?

If you have reciprocating linear motion (such as a piston moving up and down in a cylinder), is it possible to generate three-phase AC power from it without converting it into rotary motion first? I ...