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8TH CLASSES PHYSICS DAILY PLAN SUBJECT: M MA AG GN NEETTIISSM M AIM:To learn the properties of the magnets DURATION: 160 min REAL LIFE:Magnets PRESENTATION: M Maaggnneettiicc pprrooppeerrttiieess:: A magnet is an object that has the property of attracting magnetic substance. Substances, which are attracted by a magnet, are called magnetic, and those, which are not attracted by a magnet, are called nonmagnetic. For ex: Iron, Cobalt, Nickel are magnetic but Aluminum is a nonmagnetic material. (SHOW!). If you have a magnetic material you can create an artificial magnet by rubbing it with another magnet.(SHOW!). In nature a magnet is an iron oxide (magnetite) but we can produce artificial magnets in different sizes and shapes, such as bar magnet, U shaped magnet horse-shoe magnet round magnet, etc…FIGURES Some substances are difficult to magnetize. However, once magnetized, they tend to stay that way. They are permanent magnets (alnico). Temporary magnets, such as soft iron, are easy to magnetize. But they loose their magnetism very easily. M Maaggnneettiicc ppoolleess:: If a bar magnet is dipped into iron filings, it holds filings in large amount near its two ends (SHOW) This shows that, the forces, which make the fillings collect, are concentrated mainly near the ends. These two ends are called poles of magnet. Poles are always found in pairs. In another words a magnet has two poles (north and south) and there is no magnet having only one pole. Two poles have exactly the same strength of attraction. Bar magnet When a bar magnet is suspended or pivoted so that it can turn freely about a vertical axis in a horizontal plane, it turns and omes to rest approximately north- south direction. For this reason, the end of magnet that points north is called its north pole (N), and the other end is called its south pole (S). N S Bar magnet N S N S N S N S U magnet Like poles (N-N), (S-S) repel each other and opposite poles attract each other. A compass needle is also a bar magnet and shows (NS) directions. M Maaggnneettiicc FFiieelldd:: ((BB)) If a bar magnet is brought near another magnet, they apply a force on one another. The region about a magnet where its influence is understood or shown is called ``magnetic field of that magnet``. Magnetic field lines are directed away from on N pole and towards on S pole. Where the magnetic field lines are close together the field is strong and where they separated, the field is weak. At the two poles, field is the strongest. When you change the location of a test compass around a bar magnet, at any point needle of compass will show a particular direction and these shows magnetic field around a magnet is variable and has a direction. If a compass needle is located in a uniform magnetic field, the force acting N-pole is in the direction of magnetic field lines and the force acting S pole is in the opposite direction of the field lines. When iron filings are scattered on a sheet of plastic above a bar magnet become aligned in certain directions. The lines around the magnet are called magnetic field lines. The number of magnetic field lines passing through a unit surface is called magnetic field strength or magnetic flux density or magnetic inductor. N N S S N S N N Method of Producing Magnets We can make artificial magnets since natural ones are not easy to find. to do this, we stroke one pole of a bar a) by stroking: magnet along in a iron bar several times in the same direction then, iron Ñ bar becomes magnet. b) by contact: If either N or S pole of a magnet comes into contact with an iron nail then, nail becomes magnet. N S c) by induction: N S If iron nail is brought near to a magnet, because the magnetic field of an iron bar affect the nails, nail becomes a magnet for a while and can attract iron filings. . . Iron filings d) By the means of earth’s magnetic field If you place an iron bar at an angle with the horizontal and strike bar with a hammer several times. Then the iron bar becomes a magnet. Because, sudden motions of the domains in the iron bar are aligned in the direction in the earth’s magnetic field PPrroodduucciinngg EElleeccttrroo m maaggnneett By using electric current we will produce some effect of a magnet. When electric current passes through a conducting wire produces circular magnetic field lines around the conductor. When you pass this electric current through a coil, an intense magnetic field is formed. And when you enter an iron bar into the coil, the bar 1 becomes electromagnet. The Magnetic Field of the Earth N The earth is a giant magnet itself. The geographical pole and magnetic pole are not at the same place. 2100 km S N S Declination angle is between geographical and magnetic north. Inclination angle is between the magnet needle and horizontal. [Inclination angle is zero only at the magnetic equator] Magnetic filed of earth is about 10-5 T. HOMEWORK: MULTIMEDIA: electromagnetism, akademedia DEMONSTRATION: magnets, field lines EXPERIMENT: TEACHER: DIRECTOR: 2