The strength of a magnetic field is measured by magnetic flux density. Electrically charged particles are deflected in magnetic fields. Magnetic fields are created by electric currents. The Earth’s magnetic field is caused by a rotating molten iron core. A compass exploits the phenomenon of weaker magnets lining up with stronger magnets.
The measure of the strength of a magnetic field is called magnetic flux density or magnetic induction. A magnet is said to have a north pole and a south pole; Two magnets repel when like poles face each other and attract when opposite poles approach each other. Electrically charged particles are also deflected in magnetic fields.
The magnetic flux density is analogous to the characteristics of electric and gravitational fields. Electric field strength is the force acting on a body per unit charge, and gravitational field strength is the force acting on a body per unit mass. Magnetic fields are created by an electric current. Magnetic flux density (B) is the force (F) acting on a conducting material per unit length (l) and per unit current (I), which can be written as the equation B = F / I x L. The unit of magnetic flux density is called a Tesla.
A magnetic field is always generated at 90 degrees to a moving electric field. The direction of the electric current, magnetic field, and magnetic force are defined by John Ambrose Fleming’s left hand rule. Holding the first two fingers and thumb of the left hand at right angles to each other will indicate the relative directions of push, field and current. As suggested by the similarity of the first word sounds, the thumb shows the relative direction of the push and the first finger shows the relative direction of the pitch. The second finger shows the relative direction of the current.
It is possible to see a magnetic field using only a bar magnet, a sheet of white paper and some iron filings. This is done by placing the magnet under the paper and lightly sprinkling the paper with the filings. The fillings will align with the curved lines of magnetic field flux. More filings will be attracted to both ends of the magnet than the center, meaning the magnetic flux is strongest at these points. This is also the case with the earth’s magnetic field.
The Earth’s magnetic field is caused by the presence of a rotating molten iron core at its center. Its flux density is strongest at the north and south poles. Electrically charged particles from the sun are attracted to the poles, causing the northern lights, or northern lights, and the aurora australis, or northern lights.
The weaker magnets will line up with the flux lines of the stronger magnets. It is this phenomenon that is exploited by a compass, the needle of which is a very weak magnet. By convention, the south pole of the compass points to the North Pole of the Earth, but if the compass were magnetized in the opposite direction, it would point to the South Pole.
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