In other words, this fact seems to imply that a magnetic field is really just a non-fundamental relativistic version of the electric field. However, a closer scrutiny of the fields shows this conclusion to be incorrect. First of all, Special Relativity teaches us that all inertial reference frames are equally valid and equally fundamental. If two marbles roll past each other, then from the red marble's point of view the red marble is motionless and the blue marble is moving.
From the blue marble's point of view the blue marble is motionless and the red marble is moving. Both viewpoints are equally correct and equally fundamental. The fact that the two marbles see the situation differently does not indicate that there is a paradox, that physics is broken, or that one viewpoint is ultimately more right than the other. It just means that the situation is being measured in two different reference frames.
There are no "wrong" reference frames or less-fundamental reference frames in the universe. Therefore, a magnetic field cannot be only an electric field as viewed from the wrong reference frame because there are no wrong reference frames. Since there exists an inertial reference frame in which a magnetic field exists without an electric field being present, and since every inertial frame is real and fundamental, this means that a magnetic field is real, is fundamental, and is not necessarily caused by an electric field.
Share Tweet. Terrestrial magnetic field, similar to magnetic field of bar magnet tilted 11 degrees from spin axis of Earth.
More on:. More from:. Vishnu Varma R Vejayan. Read science facts, not fiction Make a donation. This is the basis for the telegraph , invented in the s by Samuel F. Morse , which allowed for long-distance communication over wires using a binary code based on long- and short-duration pulses.
The pulses were sent by skilled operators who would quickly turn the current on and off using a spring-loaded momentary-contact switch, or key.
Another operator on the receiving end would then translate the audible clicks back into letters and words. A coil around a magnet can also be made to move in a pattern of varying frequency and amplitude to induce a current in a coil. This is the basis for a number of devices, most notably, the microphone. Sound causes a diaphragm to move in an out with the varying pressure waves.
If the diaphragm is connected to a movable magnetic coil around a magnetic core, it will produce a varying current that is analogous to the incident sound waves. This electrical signal can then be amplified, recorded or transmitted as desired. Tiny super-strong rare-earth magnets are now being used to make miniaturized microphones for cell phones, Marsh told Live Science.
When this modulated electrical signal is applied to a coil, it produces an oscillating magnetic field, which causes the coil to move in and out over a magnetic core in that same pattern.
The coil is then attached to a movable speaker cone so it can reproduce audible sound waves in the air. The first practical application for the microphone and speaker was the telephone , patented by Alexander Graham Bell in Although this technology has been improved and refined, it is still the basis for recording and reproducing sound.
The applications of electromagnets are nearly countless. The same principle used by a giant crane to lift junk cars at a scrap yard is also used to align microscopic magnetic particles on a computer hard disk drive to store binary data, and new applications are being developed every day. Therefore, it can be a useful tool for helping people find their way around.
The north end of a magnet points toward the magnetic north pole. Solar wind , charged particles from the sun, presses the magnetosphere against the Earth on the side facing the sun and stretches it into a teardrop shape on the shadow side. The magnetosphere protects the Earth from most of the particles, but some leak through it and become trapped.
When particles from the solar wind hit atoms of gas in the upper atmosphere around the geomagnetic poles, they produce light displays called aurora s.
Historic Directions The ancient Greeks and Chinese knew about naturally magnetic stones called "lodestones. The Chinese discovered that they could make a needle magnetic by stroking it against a lodestone, and that the needle would point north-south.
Animal Magnetism Some animals, such as pigeons, bees, and salmon, can detect the Earth's magnetic field and use it to navigate. Scientists aren't sure how they do this, but these creatures seem to have magnetic material in their bodies that acts like a compass. The bright bands of color around the North Pole caused by the solar wind and the Earth's magnetic field. Also known as the aurora australis.
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