# Questions tagged [electricity]

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

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5answers
17k views

### How can one derive Ohm's Law? [duplicate]

I am looking for the derivation of Ohm's Law, i.e., $V$ is directly proportional to $I$. Can someone help me with it?
0answers
20 views

### Static Attachment [on hold]

How could I get stretch wrap to stick to paper or toilet paper type material? I have a stretch wrap machine that shrink wraps large rolls of paper, and the current method of attaching the stretch wrap ...
1answer
38 views

### Can temperature difference in a conductor induce charge in it?

Assume a metallic rod which is heated on its right end to maintain a constant temperature gradient in the rod. Now if we take any crossection in the rod,the right side part of the cross section has ...
2answers
60 views

### How do elecrons move?

Do elecrons move from low to high potential or they move due to attraction by positive charge? Or is it something else, what actually happens in flow of electricity.....the concept is just so ...
0answers
51 views
+50

### Stability of a dipole magnet undergoing eddy current braking in a cylindrical tube

Consider a cylindrical dipole magnet with strength $B$ undergoing eddy current braking in a conductive cylindrical tube with the axis of the magnet aligned with the axis of the tube. The magnet ...
1answer
69 views

### Why connect plug wires in a certain way when polarity changes in AC anyway? [duplicate]

In AC systems the two wires of a circuit alternate polarity many times per second. So positive and negative switch, half of the time a wire is positive the other it is negative. So why is it ...
0answers
21 views

### Determining the z-component of the electric field at a point near a plate [on hold]

I'm struggling with all three parts a,b,c. Any help would be great, thanks. Regards Roy Browning
0answers
69 views

### Doesn't electrical energy gets lost due to slackening of local electrical wires hinged between street electric poles?

I am talking about the wires which get somewhat loose or somewhat like parabolic shaped due to earth's gravity. What I think is due to slackness of wires there is a net increment in resistance which ...
1answer
359 views

### How does RPM and the Number of Coils affect a Generator output?

I’m making a simulation where the user inputs a value of force to apply to turn the generator. This is used to calculate torque and then rpm. The user can also decide how many coils the generator ...
5answers
788 views

### Why does more rapidly changing magnetic field induce greater EMF?

I am confused about the above question. I know that when you move a magnet in and out of a close loop of wire, you induce a EMF in the wire. The change of moving the wire in a out of a wire is what is ...
1answer
60 views

### How to prove that $\vec{E}$ is an intensive property?

In my homework I had a question to sort a few variables into intensive properties and extensive properties. I wrote that $\vec{E}$ (electric field) is an extensive property, thinking of a situation ...
3answers
58 views

### Found some errors in some equations of electric power. What is the actual problem?

I think the following two equations are incorrect when $I, R$ refers to current and resistance respectively and $V$ refers to potential in the difference of potential of the two sides of the resistor ...
2answers
536 views

### Voltage/Charge in a Negatively Charged Balloon

Could somebody explain the following excerpt from my Physics book? I don’t understand how, if the voltage of the balloon is so high, the charge can be so low? Maybe it’s just worded confusingly: “...
1answer
2k views

### Use of rheostat in a practical potentiometer?

In a practical potentiometer, why is a rheostat used in series to a potentiometer wire? As we move the jokey the primary circuit current will also change. So, can we cause the same amount of current ...
0answers
12 views

### MOSFET I - Vg curve [closed]

Below graph shows the I - Vg curve in the subthreshold region, Quadritica region, and linear region for 5 different transistors. I was asked to determine which I - Vg curve in the below graph is ...
0answers
17 views

### MOSFET Band Diagram from surface to substrate [closed]

The question below asks to identify the band diagram of MOSFET at different Vg. This band diagram is drawn from oxide-silicon surface to silicon substrate. my understanding is that the band diagram ...
0answers
26 views

### Do yall know how to modify the circuit shown in the figure below so that it could be used to control central heating system? [closed]

do you know how to modify this circuit so that it can be used to control the central heating system
1answer
191 views

### Earth as a conductor

In a lightning rod or other safety devices, charge is directed towards the earth. How the surface of the earth can be used as a conducting path despite being composed of material that is not a good ...
3answers
37k 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 ...
7answers
19k views

### Difference between current and voltage sources

I am confused about the current and voltage. My intuitive example would be that of a pipe of say water. The diameter of the pipe determines the amount of water flowing per second but the pressure is ...
1answer
814 views

### Electrical flow in a simple parallel circuit

I'm having trouble understanding something in one of my text books: Let’s have a look at the implications of each circuit configuration. Figure 3.13 shows the Conventional representation of a ...
1answer
23 views

### Why are the times at which max rate occurs different for the energy of a capacitor and the battery

When charging a capacitor the rate at which the battery provides energy is maximum at $t=0$ but the time at which the rate of increase in the energy of a capacitor is maximum is $t=CR\ln(2)$ (where $C$...
2answers
350 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 ...
1answer
57 views

### What causes changes in frequency in the Nation Grid electricity supply? [duplicate]

Following the power cuts in Britain this week, we were told that lack of power being generated led to a drop in the AC frequency as shown in this graph: I understand why a stable frequency is ...
2answers
159 views

### What does it means to say an electric charged person has a higher potential voltage compared to the door?

I'm studying electric potential energy and its defined as the energy needed to move a charge inside an electric field from a point $a$ to $b$. Then, it defines electric potential energy per charge, ...
1answer
36 views

### Which is induced first EMF or Electric field?

I am quite amazed by the reasoning given by my teacher about induced electric field and induced EMF.Well,the case was of a closed conducting loop placed in a time varying but uniform(in space) ...
1answer
34 views

### Two explanations of how electric motor works: are they correct?

Let's consider the simplest model for a DC electric motor: For simplicity, we assume that over a short period of time, the current through the motor is constant. All the discussion below refers to ...
2answers
250 views

### Field Theory: Electric Field

I am a grade 12 student, and we are learning electric flux. We covered electrostatic forces and, now we are on electric flux. We defined electric flux as the total number of lines of force passing ...
0answers
20 views

### Constructing an equation for the induced EMF, in terms of the radius of a circular loop [on hold]

In order to calculate for the curl of the induced electric field for a loop moving in a uniform magnetic field, and using the cylindrical coordinate system for a curl, it's my understanding that since ...
2answers
81 views

### What could cause a small shock from an umbrella being held near a lightning strike?

I was just outside holding an umbrella when lightning struck very close by. In the instant it struck, I saw and felt a little shock from the shaft of the umbrella into my thumb. It felt quite small.. ...
1answer
20 views

### Calculating the accurate emf of an electric generator

Let's consider the following simple model of an electric generator: Many textbook say the following: The magnetic flux through the coil is $\Phi=BA\sin \theta$, where $\theta=\omega t+\phi$ is the ...
1answer
40 views

### The currect density in materials of uniform resistivity

Inside an infinitely large piece of material that fills the whole $\mathbb R^3$ space with uniform resistivity $\lambda$ (which letter should I use, when $\rho$ has been used for charge density?), ...
4answers
94 views

### Resistors are used to reduce current to prevent light bulbs from “exploding” but it's also said that “current remains same at all points in a circuit”

Resistors are used to reduce current in order to prevent light bulbs and other electrical components from “exploding”, but it is also said that “current remains the same at all points in a series ...
5answers
8k 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, ...
0answers
56 views

### Interesting electric shock question

So the other day I was moving a fan and I put my hand on the wire. I got an electric shock for about 5 seconds, whilst being thrown over the sofa. Now I touched it with bare dry hands, and I had bare ...
2answers
51 views

### How exactly does fault current through a person return to the source

this question has been bothering me for a long time Say a person touch the live wire as shown in the picture, the current will flow through him and dissipates into the ground in "rings" as shown in ...
1answer
112 views

### Electricity from effervescence, is it possible?

I've had this idea for quite some time (after having a cold and seeing Tabcin sparkling tablets), is there the possibility to generate electricity from effervescence? I envisioned something like the ...
4answers
845 views

### Can touching a single power line (on the street) kill you?

Statement: You need to touch two power lines at the same time to get electrocuted. I am kinda doubting this now because, in the video linked below, it looks like the person is only touching one line ...
1answer
43 views

### 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 ...
3answers
68 views

### Why does current remain constant in a series circuit although the rate at which they flow deceases due to the collisions they go through? [duplicate]

I am really confused and frustrated as I can't figure this out. If someone could clear my doubt, I'd be really thankful. According to my textbook current is the rate of flow of charge, it is ...
1answer
41 views

### How do electrons keep moving when bare copper wires are rolled? [closed]

How do electrons keep moving when bare copper wires are rolled? When someone strips the wires and coils the copper, does that not affect the communication between the devices, that is, the bits do ...
1answer
115 views

### Electrical Conductivity of Washing Up Liquid

My question is a simple one, as I do not have the equipment to hand to test it. At standard UK household voltage, would it be reasonable to assume that, if covered in a film of washing up liquid, a ...
1answer
118 views

### How to insulate static electricity

This is a follow up question to Extending the reach of a crocodile clip for Kelvin Water Dropper experiment. We have resolved the issue, but now we have the following cable (in the image) that ...
1answer
47 views

### Regarding the force acting on a small patch on the the surface of a charged sphere

In Purcell's Electricity and Magnetism, page 30 and 31, there is a section which dealt with the evaluation of the force acting on a small patch (the tiny square in the picture) on a charged sphere: ...
2answers
37 views

### Conservation & Flow of Energy in Circuits

Before I ask my question, it's important that you know how I understand the underlying physics of circuits, so you could point out any misunderstandings or incomplete thoughts. A battery creates an ...
1answer
176 views

### What is the theoretical maximum efficiency for LEDs?

Whatever efficiency you want to give in converting electricity to light. I'm guessing it would depend on the type of LED. I imagine limitations come from various reasons. It would be cool if there ...
2answers
53 views

### What is the exact mechanism of flow of electricity?

When a steady current flows through a conductor, the electrons in it move with a certain average ‘drift speed’. One can calculate this drift speed of electrons for a typical copper wire carrying a ...
1answer
112 views

### Difficulty understanding the energy transformations during resistance in a circuit

I am currently having problems understanding the energy transformations that occur when resistance in a solid conducting wire restricts current flow. From my understanding, resistance in a solid ...
0answers
28 views

### Is equilibrium potential relative?

If you have a half cell reaction, let's say: $Zn$ electrode and ($SO_4^{2-}$ and $Zn^{2+}$) solution The solution will get more and more postive and the electrode more and more negative until \$\...
1answer
123 views

### is it resistance of filament or current thorugh it which determines brightness of bulb?

SO brightness of bulb. Does it depend on the resistance or current in it.? I have two bulbs keeping everything same except resistance. So Bulb A - high resistance Bulb B - Low resistance which ...