# All Questions

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53 views

### How does alternating current provide energy?

In my head, direct current makes complete sense; the electrons carry energy around the circuit to something being powered losing its potential and then return to the battery or whatnot to have their ...
36 views

### Why are there many turns in the primary coil of a step-up electricity transformer?

Since the voltage in a coil is proportional to the number of turns, the ratio of voltages is equal to the ratio of turns. So if you need a big increase in voltage, what stops you from having one turn ...
15 views

### Effect of a current carrying wire on a point charge

Given a point charge $q$ near a wire carrying current as shown, what would be the effect of the magnetic field produced by the wire on this point charge $q$? I think the sign on $q$ is important so ...
17 views

### Capacitance of insulated conductor with charge on insulation surface

I have an insulated wire at high voltage (10s of kV) running above a conducting ground plane. In my case, I expect that corona discharge will occur briefly after the HV generator is turned on, but ...
30 views

### In a circuit, do surface charges get influenced by external electric fields?

Hello ,This image represents surface charges in a circuit caused by the battery's electric field, if you were to place an other electric field source of the same magnitude (but not connecting it to ...
62 views

### Skin Effect Explanation

I do not understand some things about the Skin Effect. Its Wikipedia definition is: Skin effect is the tendency of an alternating electric current (AC) to become distributed within a conductor ...
25 views

### Electric field generated by disk and conductor

I'm trying to solve the following problem but I have some doubts. I have a disk of radius $R$ with charge $Q$ (positive) and, at distance $d$, an uncharged conductor (of radius $R$ as well). Both are ...
25 views

### Force on a current carrying loop

I recently encountered a question which went like this, A current-carrying loop is placed in a plane perpendicular to a long current carrying wire at a distance from it. What is the force acting on ...
60 views

### What makes the internal resistance of a battery at microscopic level?

What makes the internal resistance of a battery at the microscopic level? And why does voltage drop when in a circuit compared to the open circuit voltage? I think that the field between the ...
91 views

### Electrolyte and internal resistance

If you have a Daniell cell(zinc / copper), excess charges will build up on the electrodes making the open circuit voltage until the reactions halt. Now in normal situation when you connect their ...
70 views

### Coulomb's law experiment, why consider the distance between the body's centers?

In $F_e=\frac{1}{4\pi\epsilon_0}\frac{q_1q_2}{r^2}$, why did Coulomb consider the distance between the center of the charges? Why not the distance between the immediate outer surface between the two ...
32 views

### Do surfaces charge distribution in a wire move?

Upon reading matter and interactions ,In the chapter "electric field in a circuit" and surface charge distributions in a steady current, The book dosen't explain why doesn't the surface charges move ...
3k views

### Are the plates of a battery really charged?

In a zinc/copper Daniell cell correct me if I am wrong : Zinc has 2 valence electrons. So it wants to get rid of them. To do so it sends them to the copper which needs 2 to complete its valence ...
38 views

### What happens if you connect a wire to the anode of a battery, but not the cathode?

My understanding is that the anode of a battery is positive while the cathode is negative. If you connect a wire between the cathode and the anode, then the electrons in the cathode want to flow to ...
83 views

### What makes air a good insulator?

What makes air a good insulator? My understanding of air is that its mostly just empty space with a few molecules whizzing around. Now consider a negatively charged ball suspended in air. Why don't ...
57 views

### Why is the Earth considered an infinite electron source or sink?

All the literature I've read says that Earth is pretty much an infinite electron source/sink. If you add or remove electrons from the earth, then the charge of the earth must change. Furthermore, the ...
28 views

### Why does a surface charge experience electrostatic pressure from its own field?

In Griffiths he mentions that a surface charge experiences a force in the presence of an electric field, but then he specifies that a force experienced by the surface is one due to its own electric ...
3k views

### How can electric fields be used to detect cracks in metals? [closed]

My physics teacher brought this up in a lecture and I am not exactly sure what he is saying.
28 views

### Derivation of Magnetic Field from Infinite Wire

I'm trying to get my head around the derivation for the magnetic field of an infinite wire, in my notes I have the statement: Setup: Wire centred on the z axis, current has direction +z. "Biot-Savart:...
60 views

### What forces are acting on electron in a circuit? Do electrons act on each other in a current?

What forces are acting on electron in a circuit? What is the source of such kind of forces? Do electrons act on each other in electric current? If i have an ordinary electric circuit with only one ...
42 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 ...
13 views

### 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 ...
29 views

### 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: $2πNBAfsin(2πfT)$ ...
22 views

### 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 ...
33 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 ...
44 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 ...
28 views

### 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 ...
66 views

### 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 ...
28 views

81 views

### What is meant by “changing magnetic field”

At first I thought it was the consequence of an object moving from an area of high to low or low to high flux density, but that doesn’t help understand what is meant by “a changing magnetic field” ...
18 views

### Split ring commutators in a dynamo

Can someone please explain how they work? So far i've only been able to gather - they somehow convert ac into dc - they touch electrical brushes once a half turn (??why is that important?) -they let ...
58 views

### If electricity creates a magnetic field, could a (strong) magnetic field stop electricity? [closed]

Surely this would make the two magnetic fields interact and if movement was made impossible, the stronger magnetic field would block the weaker electromagnetic filed. Am I right (presuming that the ...
31 views

### Electrons in a conductor loosely bound or delocalised (as per QM)?

Currently there are two main ideas of those electrons that move in a conductor: those electrons moving are loosely bound to the valence shells of the atoms in the lattice those electrons moving are ...