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EEE, , i electric, The relationship between the magnetism and :, 2 ji wa!, current was first discovered by a scientist Oersted way, , back in the early years of nineteenth century., ~ He discovered that a conductor carrying a current 's, , always surrounded by a magnetic field along the length, , of the conductor. This is known as electromagnetism., , = Electromagnetism is a branch of electrical engineering, , that studies the magnetic effects of an electric current., , 1.1.1 Magnet:, , ~ _ Itis a piece of solid substance which exhibits a property, of attracting small pieces of certain materials such as, iron, steel etc., , Types of magnets :, , — Magnets are of two types :, 1. Natural magnets. 2. Electromagnets., , ~The natural magnets have the Properties of magnetism, naturally present whereas electromagnets are formed, by passing an electric current through an insulated wire, wound around a certain material., , — That material then acts as a Magnet as long as the, current is flowing. But it loses its magnetic properties as, soon as the current stops flowing., , Tagnetic induction :, , If a magnet is placed near a piece of a magnetic, material such as iron, then without any physical contact,, magnetism gets transferred to the piece of iron. This is, , called as magnetic induction., , ) Law's and Definitions :, , In this section, we are going to define certain important, , laws and parameters related to magnetism., The laws and definitions are :, 1. Pole strength., , 2, Coulomb's law., , Magnetic field and magnetic lines of force., I/agnetic flux and flux density., , Magnetic field strength., , , , 4.21. FOS, Definition :, , Pole strength i, a distance 0!, , experience:, , is the strength of a pole whic}, j, . ", , f 1 metre from an identicay, 7 4, placed at aca sa force of [10° / 165°} \, the free space,, , ole strength is a measure, the other magnet., , of the force that &, i, , - Thep, , exerted by a magnet on, , If two poles exert the same amount of force on ang,, Ww, , le then they are said to have Fetiel Beeoral, , ole £ = }, , P Je strength is measured in weber Or unit pole,, 0, , 1.2.2 Laws of Magnetism :, , are two basic laws of magnetism :, , — . There ‘, tates that the like poles repel each y, , 1. The first law s, and unlike poles attract each other., , 2. The second law is known as the Coulomb's law, nap,, after a famous scientist Coulomb., , Coulomb's law :, — — The Coulomb's law states that the force (F) exertey, one pole on the other pole is directly proportiona, the product of the pole strengths of the two poles;, inversely proportional to the square of the distance, between them., , This force is also dependent on the nature of medi, surrounding the poles., , Coulomb’ law is mathematically expressed as follows, , , , m, m2, , Fox & w(12, m, m2, , or F= K ae (12,, , - Where m, and m, are the pole strengths and K ist, constant which depends on the nature of t, surrounding material and (d) is the distance betwe, the poles., , 1.2.3 Magnetic Field :, , Definition :, , - The magnetic field is defined as the region neat, magnet within which the effect or influence of ?, magnet is felt., , , , ~The influence of a Magnet i.e. presence of m, field can be tested by using a simple Compass needes, by using an another magnet., , , , , , Scanned with CamScanner

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4.2., , Definit, , 4 Magnetic Lines of Force :, , The magnetic lines of force are used for representing, the magnetic field of a magnet. These lines, , i are, ginary and do not have any physical existence,, , ima', , they were introduced by the scientist Faraday in order, , to represent the distribution of the Magnetic field of a, magnet. The magnetic lines of force are also known as, Lines of Magnetic Flux., , jon of line of force :, , A line of force is defined as a line along which an, , isolated N-pole would travel if it is allowed to move, , freely ina magnetic field., , 4.2.5 Magnetic Flux ¢:, , , , , , , SPPU : May 12, May 14, , , , , , Q.1 Define magnetic flux and state its unit. (May 12), ia.2 With reference to a magnetic circuit explain the, terms 1. Magnetic flux, 2. Magneto-motive force,, 3. Magnetic field intensity, 4. Magnetic flux density,, 5. Reluctance 6. Permeability of free space. State, their units. (May 14, 6 Marks), Definition :, , The magnetic flux is defined as the total number of, lines of force in a magnetic field. It is denoted by and, , measured in Weber., , One weber is defined as the flux (number of lines), radiated out by a unit N-pole., , 10° lines of force ...(1.2.3), , 1 Weber, , 1.2.6 Magnetic Flux Density (B) :, , , , Jor, Q.2, , i, , ISPPU : May 12, May 14, , LT Edis, , (May 12), , Define flux density and state its unit., With reference to a magnetic circuit explain the, terms 1. Magnetic flux, 2. Magneto-motive force,, 3. Magnetic field intensity, 4. Magnetic flux density,, , 5. Reluctance 6. Permeability of free space. State, , their units, (May 14, 6 Marks), , , , a, , Definition :, , The flux per unit area (A), measured in a plane, perpendicular to the flux is defined as the flux density., , It is measured in Tesla (T) and denoted by B., , a, , Magnetic flux density B= a tesla., , 1.2.7. Magnetic Field Strength (H):, , , , , , , , EGGURIEEE, , Q.41 With reference to a magnetic circuit explain the, , terms 1. Magnetic flux, 2. Magneto-motive force, , 3. Magnetic field intensity, 4. Magnetic flux density, , 5. Reluctance 6. Permeability of free space. Stat, , their. units. (May 14, 6 Mark, Definition :, , The magnetic field strength at a point in the magn, field is defined as the force experienced by a unit Ni, pole placed at that point in the magnetic field., denoted by H., , Note that the unit N-pole is the N-pole with a, strength of 1 Wb., , Higher the value of the force experienced stronge, be the field. The magnetic field strength is measur, Newtons per weber (N/Wb) or ampere per r, (A/m) or ampere turns per meter (AT/m)., , _ Ampere - Turns, ~ Length in metre, , a, , Magnetic field strength is also called as magneti:, intensity., , 1.2.8 Electromagnets :, , , , Electromagnets is the other category of magnet:, are not natural magnets., , As shown in Fig. 1.2.1, whenever an electric «, passes through a conductor or a coil, a magnet, gets developed across it, and the coil starts actin’, electromagnet., , If the coil is wound on a piece of some m, material, then that piece will start acting as a mai, , It is interesting to know that an electromagnet |, , magnetic properties as soon as current passing |, , the coil reduces to zero., Scanned with CamScanner

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LL, The flux density can be controlled by controlling the, Magnitude of current 1., , The direction of magnetic field (direction of N pole), , depends on the direction of current flowing through, the coil., , +, , LL, , (A-432) Fig. 1.2.1 : An electromagnet, , 1, | _ Magnetic field, , , , , , , , , , , , , , , , lL Magnetic material, , Coil, , 1.3 Magnetic Effects of Electric, , Current :, , Whenever an electric current (ac or dc) is passed, through a conductor, a magnetic field gets generated., ~ If the current is dc, then the generated field is steady, , magnetic field ie. the one which does not vary with, time. ,, , ~ But if the current is alternating, then the generated field, is time varying magnetic field., ~ Fig. 1.3.1 shows the association of magnetic field with a, , current carrying conductor., Conductor, , Current, , ‘Magnetic field, (A-433) Fig. 1.3.1 : Magnetic effect of electric current, , — The field strength of the magnetic field depends on the, magnitude of current flowing through the conduction., , - Magnetic field strength increases with increase in, current., , - The direction of magnetic field depends on the, direction of current through the conductor., , 1.3.1 Dot and Cross Conventions :, , The dot and cross conventions are used for indicating, the direction of current flowing through a conductor., , 1. Cross convention :, , If the current flowing through a conductor is moving, , away from the observer and into the plane of paper as, , , , shown in Fig. 1.3.2(a), then this current direction, 5, , indicated by a cross (X) as shown in Fig. 1.3.2(b)., , - Generally the tail of an arrow indicating curren, ., i, , indicated by a cross. In Fig. 1.3.2(a) the observer any,, , the tail of the arrow. Hence a cross is used., , , , , , , , , , Observer, @, , A, , | Current, ‘Conductor, Paper Oo, Current, Conductor —, (a) (b), , (A-435) Fig, 1.3.2 : Cross convention, , 2. Dot convention :, , - — If the current flowing through a conductor is Moving, , towards the observer or coming out of the plane g, paper as shown in Fig. 1.3.3(a), then this currey, direction is indicated by a dot as shown in Fig. 1.3.3(b),, , - Generally the tip of an arrow indicating current 5, indicated by dot. In Fig. 1.3.3(a), the observer can'se, , the tip of the arrow. Hence a dot is used., Observer, , @, , A, + Current, , Conductor, , ©, , , , Paper, , , , , , , , , , y Current, Conductor, , (a) (b), (A-434) Fig. 1.3.3 : Dot convention, , Conclusion :, , - Thus a dot represents current coming out of the pla®, , of the paper while a cross represents current enterift, into the plane of paper when observed from the tof, , This is shown in Fig. 1.3.4., , el, Scanned with CamScanner

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©, , current flows i Current flows out, nto the plane e ihe Of the plane of paper, f away from and towards the observer,, , an, paper opsorver, , ross convention (b) Dot convention, , c, (a) (A-436) Fig. 1.3.4, , 4.3.2 Rules to Decide Direction of Magnetic, Field :, , in order to determine the direction of magnetic field, associated with the current flowing, , conductor, we can use the following rules :, , through a, , 1 the right hand thumb rule and right hand Gripping rule., , 2, The corkscrew rule., , 4.3.3. The Right Hand Gripping Rule, “(or Right Hand Thumb Rule) :, , Statement‘, As shown in Fig. 1.3.5 if a straight current carrying, conductor is held in the right hand such that the thumb, indicates the direction of current then the other fingers, curled around the conductor point the direction of, , magnetic field., , Fingers indicates, the direction of field, , Conductor, , , , , Current, , Direction, of field, , (A-437) Fig. 1.3.5 : The right hand thumb rule, , Stretched thumb points, the direction of current, , 1.3.4 The Corkscrew Rule :, , Statement :, , ~ Consider a right handed screw or wood screw shown in, Fig. 1.3.6(a)., , When this screw is to be inserted in a wooden plank, it, Must be rotated in the clockwise direction. If the, direction of advancement of the screw indicates the, direction of Current, then the circular rotational motion, , Of the screw indicates the direction of the magnetic, field, , , , Direction of rotation, indicates the direction, , aN J of field, , , , , Direction of travel, / indicates the direction, of current, , |!, , (a) Corkscrew rule, , if, , Magnetic, , feld, , , , , , Current Current, flowing into coming out, the plane of of the plane, , paper of paper, , (b) Dot and cross conventions, (A-438) Fig. 1.3.6, , | = Fig. 1.3.6(b) shows the direction of magnetic field, , associated with a current carrying conductor for, different current directions., , 1.4 Magnetic Field Associated with a, Straight Conductor :, , Statement :, , - Whenever a long straight conductor carries current, it is, always surrounded by a magnetic field., , - The lines of forces form concentric circles in the planes, which are at the right angles to the conductor and, direction of lines of force depends on the direction of, , current as shown in Figs. 1.4.1(a), (b), (c) and (d)., Explanation (Refer Fig. 1.4.1(a)) :, , - Fig. 1.4.1(a) demonstrates the generation of magnetic, field due to current flowing through a straight, , conductor into the plane of cardboard., , - The pattern followed by the lines of force can be, , obtained by sprinkling iron fillings on a cardboard, , Scanned with CamScanner

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Fig. 1.4.1(d) shows the other way of representation,, , placed exactly at right angles to the direction of the, The “dot” inside the conductor indicates that th, , current flow., current is flowing out of the plane of paper i.e. toviar., , This can be shown in a different way by drawing the top, the observer., , view of Fig. 1.4.1(a). In Fig. 1.4.1(b) the conductor is, The direction of magnetic field is anticlockwise as ny, , drawn at the center., the right hand thumb rule., , The “x” sign indicates that the current is flowing into, , , , the pla f .e. 8 from the observer. And the, plane of paper, i.e. away fr Magnetic fiel, , , , , , , , , , , , , , , , , , direction of magnetic field is clock-wise as per the right Current Symbol +i, direction direction, hand thumb rule., = Into the paper Cross Clockwise |, Explanation of Figs. 1.4.1(c) and (d) : 0 |, 5 Coming out of Dot Anticlockwise, As the direction of current is reversed as shown in, i ; . ; aper, Fig. 1.4.1(c), the direction of magnetic field is also Eee, reversed. However its shape remains unchanged., Direction of, magnetic field, Top view, , , , , , -— Conductor, , I Current 1, , Pattern of iron, fillings, Direction of field, , , , , , , , , , , , , , , , , , , , , , , carubeat? — + Indicates that the, L current is flowing into, Conductor Current! the plane paper, (a) Magnetic field due to current flowing (b), through a straight conductor, Direction of, magnetic field, | ee I, Conductor, Pattern of iron, fillings, , ! Direction of field, , , , , , , , NS Cardboard /— « Indicates that the current, is flowing out of the plane, , t. Top view, Current I of paper, , (c) Direction of magnetic field is reversed (d), due to change in current direction, , , , Conductor, , (A-439) Fig. 1.4.1 : Magnetic field associated with a straight conductor, Scanned with CamScanner