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2
votes
2answers
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 ...
2
votes
1answer
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 ...
1
vote
1answer
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 ...
0
votes
0answers
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 ...
0
votes
1answer
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 ...
2
votes
1answer
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 ...
1
vote
1answer
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 ...
0
votes
0answers
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 ...
1
vote
1answer
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 ...
1
vote
2answers
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 ...
4
votes
1answer
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 ...
0
votes
2answers
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 ...
17
votes
4answers
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 ...
0
votes
2answers
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 ...
1
vote
4answers
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 ...
1
vote
1answer
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 ...
0
votes
0answers
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 ...
15
votes
1answer
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.
0
votes
2answers
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:...
2
votes
1answer
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 ...
0
votes
1answer
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 ...
0
votes
0answers
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 ...
0
votes
2answers
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: $2πNBAfsin(2πfT)$ ...
0
votes
1answer
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 ...
0
votes
1answer
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 ...
1
vote
2answers
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 ...
0
votes
0answers
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 ...
2
votes
3answers
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 ...
0
votes
0answers
28 views

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: $\...
1
vote
1answer
28 views

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 ...
2
votes
1answer
85 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 $\...
0
votes
2answers
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” ...
0
votes
0answers
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 ...
2
votes
1answer
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 ...
1
vote
1answer
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 ...
0
votes
0answers
42 views

What is the analogue of a dielectric in magnetism?

Capacitors and dielectrics pertain electric phenomena, one could say that inductors can be considered analogues of capacitors in the magnetic case. Is there a dielectric analogue in magnetism? What ...
2
votes
2answers
80 views

Resistance of an object with arbitrary shape

Suppose to have a conductor with a non-trivial geometry, like the one in the picture: The shape does not really matter for this question, as long as you suppose to have at least one "hole" in the $z-...
0
votes
1answer
33 views

What is the change in the form of energy that is shown by the change in direction of the compass needle when an electric current is passed beneath it?

If the magnetic field generated by the electric current does not move the compass needle, no work is done, thus no energy is exchanged. If the magnetic field generated by the electric current does ...
0
votes
0answers
14 views

Current through the secondary of a transformer

If I know the wattage of the primary of a transformer, and the input voltage, how do I calculate the current flowing through the secondary, if a load of some resistance is placed across the secondary?
0
votes
5answers
115 views

Does V=IR define resistance for any conductor? [closed]

Just wanted to confirm if the statement is always true or not
0
votes
0answers
22 views

How does electricity flow through batteries connected in a series circuit?

From what I’ve learned, a single battery hooked up to a closed circuit will allow the free electrons built up at the anode of the battery to travel from the wire to the cathode of the same battery, ...
2
votes
0answers
40 views

Question about action-reaction pair of two wires carrying current in the same direction

Imagine two wires lined up so that they are parallel, and that they both have a current running through them in the same direction. The magnetic field produced by the current of one of the wires (say,...
0
votes
2answers
65 views

Magnitude of an electric field on a long rod [closed]

You place $2.7 \: \rm \mu C$ of charge along a long nonconducting rod. The rod extends from $x=0$ farther than you can see along the positive $x$ axis. The charge distribution has the form of a ...
0
votes
0answers
47 views

If we're wearing a metal watch, do we get an electric shock on our wrist when we're charged and touch a conductor?

As the charge would flow to/from the watch, assuming I'm insulated from the ground with rubber soles, or standing on glass.
2
votes
2answers
193 views

Voltage Drop Explanation. Is it correct?

When the battery is turned on, a wave propagates within the circuit to determine the current of the sytem.At this point, the current is inhomogeneous withing the circuit(but this dissapears almost at ...
1
vote
4answers
140 views

Basics of electric current

I am a mathematician who never took a physics class besides classical mechanics. Recently I have been looking at biophysics for a small project and I have a hard time understanding the basics of ...
0
votes
0answers
36 views

How do scientists determine the width a thunderbolt?

As I searched on the internet, I found a website stating that the width of a typical lightening strike is $2.5~$cm wide and $8$ km long. I intuitively understand that scientists can measure the length ...
1
vote
0answers
36 views

why doesn't EM waves get weaker as we travel further away from the source [duplicate]

I know that as we get further away from the charge or from the magnetic field source both magnetic field and electric field decreases ,so why don't electromagnetic waves get weaker as the travel ...
0
votes
1answer
52 views

Center tap transformer- How do we get voltages that are 180 out of phase?

I have been reading that in a center tap transformer, we get 2 voltages which are 180 out of phase. Can someone please explain how that happens.?
0
votes
0answers
223 views

Magnetic field at the center of a rotating charged square loop

Consider a square loop of side length $2a$, with a total charge $Q$ uniformly distributed along its sides (so that the line charge density is $\lambda=\frac{Q}{8a}$), set spinning at angular velocity $...