Electricity and magnetism are closely linked by maxwell equations But other that we still have not found any magnetic monopoles (no, not those quasiparticles in spin ice, they don't count), is there any other significant difference between them? Background of this question Learning some solid state chem at uni Learnt of phenomenons such as Ferromagnetism Ferrimagnetism Diamagnetism (Antiferromagnetism) Paramagnetism Heliomagnetism Frustrated states (spin ice, spin liquid, spin glasses) Exchange spin magnets Spin ladders Spin canted magnetism Giant magnetoresistance Pyroelectricity Piezoelectricy Ferroelectricity Diaelectricity (Antiferroelectricity) Paraelectricty Helioelectricity Multiferrocity Google searching give me more stuff to fill in the gaps Ferrielectricty (All links leads to a journal describing a compound AgNbO3) Piezomagnetism Pyromagnetism (rare: http://jap.aip.org/resource/1/japiau/v29/i3/p563_s1?isAuthorized=no) Quantum electric dipole glass (http://iopscience.iop.org/0295-5075/88/2/27001) Giant electroresistance (http://www.nature.com/nature/journal/v460/n7251/full/nature08128.html) Phenomeon that I cannot find any analogue in google search Frustrated states (spin ice, spin liquid) Exchange spin magnets Spin ladders Spin canted magnetism This caused me to revisit the question on the subtle difference between electricity and magnetism google search result mainly said they only striking difference is the absence of magnetic monopoles
I seem to recall learning once that magnetism is the effect that Special Relativity has on electric charges moving relative to one another. Something to do with Lorentz contraction altering charge densities in one wire, as seen from the reference frame of the moving charges in the other wire. But don't ask me for the details.
Yes. For example, the magnetic force has the property of being velocity dependent - its magnitude is equal to qvB, where q is the particle's electric charge, and B is the magnetic flux density. Magnetic fields are also generated by moving electric charges, and so a frame of reference can always be chosen to eliminate a particle's magnetic field (more on that in a moment). Additionally, the magnetic force acts perpendicular to the direction of motion, and so tends to cause particles travel in orbits, like in a cyclotron. Also, magnetism can be used to produce the Hall Effect. The relationship between the E and B field can be described, as exchemist noted, with special relativity. In a frame of reference in which two particles are at rest, there will be no magnetic force in between them, but there will be an electrostatic force. So, consider a wire of charge of length l and a with a current I, and a particle of charge q. In a frame O in which the velocity of q is a positive number, v, the magnetic field generated at a distance r from the wire can be seen from the Bio-Savart Law B = μ₀I/2πr Since the force on q has a magnitude of F = qvB, the force is equal to F = -qvμ₀I/2πr Where the negative sign indicates that the force is attractive. Now, boost to a frame of reference O', at rest with respect to q. So, in this frame v = 0, and magnetic force exists on the particle. However, there must be a force in O' that does act to attract q to the wire, as events are independent of the frame of reference. In O', however, the wire must undergo Lorentz contraction by a factor of γ. So, the spacing in between charges in O' is equal to l/γ. Let's say that the wire consists of N charges per unit of length in O. Then, as per the mentioned length contraction, there must be γN charges per unit length in O'. If the charges in the wire possess an electric charge e, then the Lorentz transformation changes the current density as λ → λ' λ' = (γNe - Ne/γ) = Ne(γ - 1/γ) = -γNe(1 - 1/γ²) = -γNev²/c² The current I in O is given by I = Nev. Therefore, the above charge density can be rewritten as λ' = -γNevI/c² Since the electric field of a charged line is given by E = λ/2π∊₀r, the E field in O' is E' = λ'/2π∊₀r = -γNevI/2π∊₀rc² Then, we can use the fact that the relationship between the speed of light and the vacuum permeability and permittivity is c² = 1/μ₀∊₀, the above takes the form E' = -γv(μ₀I/2πr) The electric force on q is then F' = qE' = -γv(μ₀I/2πr) Which is identical to the force in the frame O up to a factor of gamma. So, Lorentz transformations transform electric fields and magnetic fields into each other. For components perpendicular to the direction of motion, the relevant equation was derived above E' = -γv(μ₀I/2πr) E' = -γvB So, the difference between E and B fields is that of the frame of reference. Therefore, the fundamental quantity is not the electric or magnetic fields, but the electromagnetic field.
@Secret hopefully they've let you experiment in the lab instead of just reading textbooks all the time.
They have labs, but my curiosity result in pretty much every time I look up information after lectures and labs, I end up having a new question. (I basically asked my professors as much questions as in this forum) @MarkM125: thanks for the info. I still need to get my head around relativity though. So basically the two major difference is 1. No magnetic monopoles 2. Magnetic force is frame dependent?
Yes, those are both distinct differences. The magnetic force is determined by the velocity of the charged particle, so, in the particle's rest frame, it doesn't create a magnetic field. Relativity isn't critical to EM, I was just elaborating on a point made by exchemist in regards to how relativity explains the frame dependence of the magnetic field.
