why a conductor does not produce e.m.f when rotated in earths magnetic field?
918766
It does, but the Earth's magnetic field strength is very weak so the resulting emf is too small to be noticed.\n\nThe strength of the field at the Earth's surface ranges from less than 30 microteslas (0.3 gauss) in an area including most of South America and South Africa to over 60 microteslas (0.6 gauss) around the magnetic poles in northern Canada and south of Australia, and in part of Siberia.\n\nSo let's assume that we have a simple setup that can induce an EMF from Earth's magnetic field:\n\nEMF = -dΦ/dt, where Φ is the magnetic flux\n\nIf we consider a very simple case where Φ = BA, where B is the magnetic field and A is the surface area. So let's assume that\n\nB = 60 microTesla = 60 x 10^-6 Tesla or 0.00006 T\nA = 1 square meters\n\nand let the time duration of the manetic flux change be = 1 sec\n\nThen EMF = |-dΦ/dt| = BA/t = (0.00006)(1)/(1) = 0.00006 Volts\n\nAs you can see, I had to let the area of the magnetic flux be rather large (1 square meters). To see any sizable effect, we would actually need to consider much much bigger area, maybe like a square kilometer.
370991
When a magnet rotates around a conductor, it generates a current in that conductor. \n\nCurrent itself is actually the electrons in the conductor moving. Some of this momentum for each electron is lost when it collides against an adjacent electron or in moving against the repulsive force between them. The sum total of all this energy lost by all the electrons is seen as heat and the conductor heats up.
441745
When you move the card through the reader pulses of current (not voltage) are generated in the coil(s) which reads your card (the Faraday effect).  The more quickly the card moves through the reader, the higher amplitude current is generated.  If you move the card too slow, the current generated is too small, and then the electronics attached to the read coil(s) cannot see a signal large enough to be detected as pulses which are interpreted as the 1's and 0's of the data on your card.\nTry the first link below and move the magnet slowly and quickly and observe what the difference is on the meter.
129623
The dynamo theory (that the earth is maganetic) is actually due to the fact that the outer crust is molten iron.  This iron is moving around inside the earth at very high temperatures.  Physics tells us that moving metals will create  a magnetic field.  This is why we have the magnetic field around the earth.
827354
The magnetic field of Earth is caused by molten iron rotating around in the core.  The lines of magnetic flux follow the right-hand rule (RHR).  Curve the fingers of your right hand into a loose fist and extend your thumb upward.\n\nAs the molten iron swirls around in the direction of your curled fingers, the flux is emitted in the direction of your extended thumb.  The flux is created because the swirling molten iron creates an electrical current that follows the swirl.  That current, like a current going through a coil, creates the magnetic flux.\n\nA flux is simply a line of force and that force, like all forces, has direction.  In this case, the force points outward in the direction of your thumb.  That's called the magnetic north pole, by convention.  \n\nHowever, because the magnetic flux exits the Earth at this pole it really is the south pole.  This can be verified because the north pole of a compass needle will point north and, as you well know, north is attracted to south.  Thus, the magnetic north pole is really the south pole...argh...physics is so complicated.\n\nAs to why like poles repel and dissimilar poles attract, blame in on the direction of the forces...the flux of that magnetic current.  (Magnetism does not really flow, but the forces act as though it does.)  Two similar poles either push each other away (e.g., two south poles) or pull away from each other (e.g., two north poles) because the forces are toward or away from the two magnets respectively.  Two dissimilar poles attract each other because the alligned forces pull one toward the other when they are all in the same direction.  [See source.]
177385
It's incredible how many crazy answers are given on this page. \nThe Earth's magnetic field is originated by the convection of molten iron and nickel within the outer planetary core.\nSo, the answer to your question is that the only way to switch off the Earth's magnetic field would be to freeze all that liquid metal. This will happen naturally by the way, but in some billion years.\nAnd tell us, why are you asking this?
473172
You've actually got several concepts and questions merged together.\n\nWhen you ask "how does the aerial setup the waves from only the ac signal?"  I assume you're asking how any DC components of the signal get filtered out?\n\nA transverse electromagnetic wave involves both a VARYING electric field and a VARYING magnetic field, appearing at right angles to each other and to the direction of travel of the wave.\n\nAny DC component has no varying component, therefore, no wave is generated.  Although DC flowing through a wire creates electric and magnetic fields, no wave is generated because there is no variance in the fields.  \n\nThere are other electronics concepts that require the changing electromagnetic fields of AC to work.  A transformer uses AC, not DC.  A capacitor will block DC signals, but allow AC signals to pass.\n\nAlso, as you indicated, an efficient antenna has a matched impedance to the signal source in order to maximize the amount of engergy propagated by the antenna in the desired direction(s).
621661
When a charge is moving (current), around its path, there is always eclectic and magnetic field. Energy is stored in these fields.\n\nWhen there is uniform current (no change of current) there is no change in the magnetic field.\n\nBut if the current changes, the energy stored in the magnetic field is spent to oppose the change of current.  That is, the magnetic field varies; eclectic field is induced.\n\nWhen there is a variable current or when a charge is pulsating, there is continuous exchange of energy between the electric and magnetic fields.\n\nAs at every instant there is a change   in these fields we don’t distinguish them as electric or magnetic; but we say that it is electro- magnetic energy. The changes in these fields are transmitted in space. \n\nIn a given volume of space there is full of electro-magnetic field and as the source (pulsating charge or oscillating current) continuously working, energy enters and leaves the volume of space under consideration.\n\nHence there is always electro magnetic energy in a given volume of space and at the same time energy is flowing in and out of the space under consideration.\n\nThis we say radiation of electro magnetic radiation.
71697
Electricity generated by relative motion of a magnetic field and an electric charge.\nMaxwell's 2nd equation states that a magnetic field that varies at a given point induces an electric field that exerts a force on an electric charge.  This force moves the charge.  The free electrons in a conductor are such a charge, and are moved by the relative motion of the conductor and the magnetic field.  \nGenerators and transformers are common applications of this effect.  In a generator the magnetic field may be intrinsically constant (created by DC or a permanent magnet), or varying (created by AC).  The conductor is a coil or set of coils.  No mechanical relative motion of the field and conductor is needed if the field is intrinsically varying.  If such relative motion is needed, the coil can be rotated with the magnetic field held stationary or vice versa, so relative motion of the conductor and the magnetic field occur.  \nIn a transformer the current is always AC and no mechanical motion is needed.  The magnetic field is produced by an input coil (an electromagnet), which shares its core with the output coil for good magnetic field coupling.
915719
Subatomic particles do not spin on their axis. What is called spin is actually a misnomer, given because it was originally thought that the only origin of the megnetic moment of the particles could be that they spin on their axis. In fact, spin magnetic moment arises naturally out of the Dirac equation (the relativistic form of the Schroedinger equation) with no rotation at all.\n\nThe Earth spins because the cloud of matter that it and the solar system condensed from was rotating, and angular momentum is conserved.
805635
it is generated through an AC generator which contains one rotor an two magnatic poles.\nin deatil:-\nwhen a coil of soft magnetic substance moves in a magnetic field it cuts the flux of magnatic field and as a result of it and the equation EMF=b*l*v AC current produces\nwhere b is magnatic strength,l is lenth of coil v is velocity or rotational velocity of coil in magnetic field
1110951
hi dear friend\n         Absolutely the earth has magnetic energy naturally.because for example if we take an hydroelectric power plants the electricity is produced from the up to down fall of water on the turbines it is due to the magnetic property of the earth.Imagine if this hydro-electric power plant is built on the moon then how the water can flow think about it  there is no gravitational feild on moon.then water drops fall is very slow imagine how u can generate large amount of power.\n                                why iam saying this is upto my knowledge there is no other instruments to derive the large amount of free magnetic enery from the earth.if we want to find such kind of instruments we have to send lot of moneys.The only thing is by using friction due to magnetic propery of earth we can able to generate small amount of electrical energy\nfor example:\n             If u see in cycle dynamo it is kept in touch with the cycle tiers.Due to friction the cycle tiers is running and there will be little amount of current will be generated for lighting purpose.
356764
The earth is actually, as a whole, a conductor, mostly because there's a lot of earth to be a source and sink of charge. That's why many high power appliances have a third prong to plug into the wall called a "ground" (the round one below the the two flat prongs). That does actually connect into the earth. That way, if there is a malfunction, the current flows done to the earth, rather than you (which generally is not fun).\n\nIf the earth were a dielectric, current wouldn't flow at all to the earth, and so the current would have to flow somewhere else (possibly you).
927344
I use one underground regularly.  The magnetic field pervades the whole planet.  Magnetic objects or rocks can distort the measurements, but they can at the surface too.\n\nEven if you were so deep underground that your compass was above the Curie Point and lost it's magnetism (in which case you would be dead as that is over 500 degrees), you could still use a fireproof electronic flux-gate compass, as the magnetic field is generated by the molten iron core (nobody is exactly sure how), so the field is present at all temperatures.
911083
The references are a good place to start learning about the earth's magnetic field.  The field on earth's surface is affected by local geologic conditions.  As your altitude increases, the earth's magnetic field looks like the field of a bar magnet.  It will cause rotation in a bar magnet that's free to rotate.  That's how a compass works.  The calculations get complex.  Try looking at a textbook on magnetism.  You'll probably see it worked out as an example.  The force in the form of a torque will be a function of the angle between the bar's magnetic axis and the background magnetic field.
127751
By behaviour of magnetic field associated with any electric conductor, the field is at right angle to the direction of flow of current. Means if current flows along X Axis, magnetic field's plane lies in YZ plane.\n\nVice a versa, if changing magnetic field is in YZ plane and a conductor is placed in the area of influence of field, current is induced in the conductor which flows in the direction of X axis. Well, these are basics.\n\nIn any magnetic device like transformer, motor or choke this principle is used. To strengthen the magnetic field, magnetic materials such as Iron cobalt etc are used. Electric conductors are arranged in these devices in such a way that magnetic field produced by electric current is at picked up by the magnetic material which are called as "Core". When magnetic field produced by electric current, magnetizes this core and the current causing the field is "Oscillating" the magnetic field associated with current also oscillates. The core material whether it be Iron or Cobalt, is a metal. It may not be as good a conductor of electricity as copper or silver or gold, but it is a conductor and not insulator. This oscillating field within the core produces induced current within the core itself.\n\nSince any electric current flow finds the shorted least resistance path, this induced current circuit closes in a small loop and in this process many small loops of current are formed in the core. This is similar to circulating air in a whirlpool or eddys prodcued in the water when you drop a stone in the water. Hence these current loops are called Eddy Current.\n\nThese small loops of current, circulating in small circles cause heat to be developed which heats up the core. Since there is also a magnetic field associated with these current loops, and is in opposite directiont of the main field, it results in reduced magnetic field density etc etc.\n\nHowever, in induction heating furances this unwanted phenomenon is put to use.\n\nIs my answer just that what you are looking for?
1182896
Voltage applied to the primary coil of a transfer causes an electrical current to begin to flow, and that causes a magnetic field to form.  As the voltage drops back to zero and reverses, the field collapses and then forms in the opposite direction.  This changing magnetic field induces a voltage in the secondary coil.  If that coil is connected to some load, the voltage causes current to flow.\n\nIf the ferromagnetic core which concentrates and contains the magnetic field is laminated, and there is some room for these laminations to move, they move in response to the changing magnetic field.  If there is no movable magnetic material in the field, you hear nothing.\n\nIt need not be harmonic.  It depends only on how the magnetic material is affected by the force applied to it by the magnetic field, and that field depends on the variation of the applied voltage with time.  It need not be the sinusoidal pattern at 50/60 Hz of commercial power mains.  In a switching power supply, it's a square wave.