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Results tagged with electromagnetism
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user 1325
The classical theory of electric and magnetic fields, both in the static and dynamic case. It also covers general questions about magnets, electric attraction/repulsion, etc. Distinct from electrical-engineering.
2
votes
Applying Ampere's Circuital Law to a bar magnet
The solenoid and the bar magnet generate their magnetic fields using different mechanisms, so the solenoid equation cannot be applied to a bar magnet.
A moving charge, like an electron, generates a ma …
- 358k
3
votes
What non-metal is attracted by a magnet?
Sticking to ferromagnetism, http://en.wikipedia.org/wiki/Ferromagnetism#Ferromagnetic_materials has a list of ferromagnetic materials. Several metal oxides are ferromagnetic - I don't know if you'd co …
- 358k
3
votes
How can there be a voltage across two wires in a circuit, if the wires has no capacitance?
To a surprisingly good approximation the conduction electrons in a conductor behave like a fluid. This is known as the free electron model. This fluid can be compressed, and indeed this is exactly wha …
- 358k
8
votes
Accepted
If inductor can store energy why not a current carrying wire?
A straight wire carrying a current does indeed store energy in a magnetic field so it does have an inductance. For example see Derivation of self-inductance of a long wire.
However the inductance of …
- 358k
3
votes
Accepted
Naive Question About Batteries
Richard Terrett's comment gives the correct answer: Richard, you should post it as an answer so people can upvote it.
A battery does indeed have excess charge at it's terminals, and the charge is sim …
- 358k
1
vote
What happens when a ferromagnetic object encounters a field too strong for it?
In a ferromagnet the field is the result of the aligned elecron spins. Once the spins are all aligned the field cannot be made any stronger. You could put a piece of iron in an external field more pow …
- 358k
5
votes
Why is the magnetic field proportional to distance?
Because there are no magnetic charges the simplest system that can generate a magnetic field is a dipole. The field from a dipole (magnetic or electric) falls off as $1/r^3$ rather than $1/r^2$ so the …
- 358k
3
votes
Accepted
Why can't electrons leave negatively charged objects in a vaccum?
Matter is full of positively charged protons, and those positively charged protons attract the negatively charged electrons. In general, if you take a chunk of neutral matter and add one extra electro …
- 358k
1
vote
Accepted
Liquid electromagnet
If you start with a coil with nothing inside it then introduce a core of relative permeability $\mu$ the effect is to multiply the strength of the generated magnetic field by $\mu$.
So in your case t …
- 358k
3
votes
Hard disk rotational frequency
The power supply to a hard disk is DC not AC (5V and 12V) and the disks themselves are heavily shielded from external magnetic fields - for obvious reasons! So there is no interaction, adverse or othe …
- 358k
3
votes
Gravity and electromagnetism
Light does curve spacetime. This is discussed in the question Does a photon exert a gravitational pull?.
In many cases we are describing the interaction of very massive bodies with much lighter ones, …
- 358k
2
votes
Deflection the needle of moving compass by magnetic field
Just for the record, and this is really just a reprise of Jonas' answer and the comments:
a current flowing and the compass is stationary:
in the rest frame of the compass there is a flow of negativ …
- 358k
2
votes
Current Electricity and E.M.F of a cell
Suppose you consider the popular analogy of a water pipe circuit with a pump supplying power and a turbine or something similar for the water to do work on. The water flows in a loop, so the net work …
- 358k
0
votes
When the load on a motor, say DC motor, is fixed, what is the relationship between torque an...
If we ignore resistive losses, the electrical power input to the motor must equal the mechanical power generated by the motor. You state that the torque exerted by the motor increases, and the only wa …
- 358k
2
votes
Accepted
why do electromagnetic waves have no charge?
The oscillation is not an oscillating charge but an oscillating dipole, and a dipole has zero net charge.
NB this doesn't mean a light wave is actually a pair of equal and opposite charges. It just t …
- 358k