Magnetism PDF

11P'" Net Unit 4 Magnetism Loop of area A 1., Introduction: I In 1269, Pierre de Maricourt of France found that the directions of a needle near a spherical natural magnet. Subsequent experiments showed that every magnet, regardless of its shape, has two poles, called north (N) and south...

11P'" Net Unit 4 Magnetism Loop of area A 1., Introduction: I In 1269, Pierre de Maricourt of France found that the directions of a needle near a spherical natural magnet. Subsequent experiments showed that every magnet, regardless of its shape, has two poles, called north (N) and south (S) poles. I If a bar magnet is suspended from its midpoint and can swing freely in a horizontal plane, it will rotate until its north pole points to the Earth's geograpiiic North Pole and its south pole points to the Earth's geographic South Pole. Although the force between two magnetic poles is otherwise similar to the force between two electric charges, electric charges can be isolated (witness the electron and proton), whereas a single magnetic pole has never been isolated. That is, magnetic poles are always found in pairs. All attempts thus far to detect an isolated magnetic pole have been unsuccessful. No matter how many times a permanent magnet is cut in two, each piece always has a north and a south pole. N S N s iS N _r N CamScanner -41-::-39,2) Introduction: If a compass needle is supported by bearings that allow it to rotate in the vertical plane as well as in the horizontal plane, the needle is horizontal with respect to the Earth's surface only near the equator. As the compass is moved northward, the needle rotates so that it points more and more toward the Earth's surface. Finally, at a point near Hudson Bay in Canada, the north pole of the needle points directly downward. I It is approximately 1300 mi from the Earth's geographic North Pole, and its exact position varies slowly with time. All substances are composed of atoms with a positively charged nucleus around which negatively charged electrons revolve. The movement of these negative charges creates small electric currents, causing an atomic magnetic field with an atomic magnetic moment. Introduction: el In the absence of any external magnetic field, small currents in different directions are random, as in Figure (9 12), which causes the creation of specific atomic magnetic fields in the size of the atom, and the resultant currents and magnetic moments in the material cancel each other out, and thus no trace of the field appears Magnetic. An exception to this case is permanent magnets. However, if the material is placed in an external magnetic field, induced by B, the magnetic force acting on the moving charges changes the direction of the orbit of the electrons in the atoms and the path of the current for the free electrons in metals. Therefore, a magnetic field is generated whose direction is with the direction of the externalfield, as in the case of paramagnetic-materials as In Figure 9 (2b), or in the opposite direction of the external field, as in the case of diamagnetic materials CamScanner -4 1-39,2) Introduction: Magnetic field Diamagnetic material  000  000  000 El=0 HAD N MS rilD°M 4//1101411D1 Paramagnetic material H=o Magnetic field II MD N m I S N CP Unit 4 Magnetism Magnetism, phenomenon associated with magnetic fields, Magnets, or the magnetic fields created by moving electric charges. the force of magnetism can attract or repel other magnets, and change the motion of other charged particle. Definition and properties of magnetic field The magnetic field is the region around a magnetic material or moving electric charge within which the force of magnetism acts. Magnetic fields are represented using magnetic field lines, see figure (4.1). 1 uamscanner -41-::-39,2) Fig. (4.1) Magnetic lines of force of a bar magnet Some important properties of magnetic field The tangent drawn to the magnetic field lines gives the direction of the magnetic field. The closeness or density of the field tines is directly proportional to the strength of the field. Magnetic field lines appear to emerge or start from the north pole and merge or terminate at the south pole. Magnetic field lines never intersect with each other. Magnetic field lines form a closed-loop. Field lines have both direction and magnitude at any point on the field. Therefore, magnetic field lines are represented by a vector. = vector quantity) They denote the direction of the magnetic field. The magnetic field is stronger at the poles because thCfieldTineg are denser near the poles. A CamScanner -4 1-39,2) Magnetic Flux Magnetic flux is defined as the number of magnetic field lines passing through a given closed surface. It provides the measurement of the total magnetic field that passes through a given surface area. Here, the area A under consideration can be of any size and under any orientation with respect to the direction of the magnetic field. Magnetic flux is commonly denoted using the Greek letter Phi or Phi suffix B (1) or (Ps). The SI unit of magnetic flux is Weber (Wb). Magnetic flux formula is given by: (PB = B A BA cos 0 Where, me is the magnetic flux. B is the magnetic field. A is the area the angle between B and 71)at which the field lines pass through the given surface area. a Consider the special case of a plane of area A in a uniform field B that makes an angle 0 with dA. The magnetic flux through the plane in this case is CPB = BA cos 9 If the magnetic field is parallel to the plane, as in Figure a, then 0 900 and the flux through the plane is zero. If the field is perpendicular to the plane, as in Figure b, then 0 = Cr and the flux through the plane is BA (the maximum value). CamScanner -41-::-39,2)