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In the first part we are going to show : • The magnetic phenomena • The magnetic poles • Field lines • The differences between the magnetic and the electric field THE MAGNETIC PHENOMENA We know that in nature there are some ‘ferromagnetic materials’ which can be magnetized. For example, the magnetite attracts iron: if we accost a bar of iron to the magnetite, it becomes a magnet. THE MAGNETIC POLES Each magnet has two poles : the north and the south. Similar magnetic poles repel each other, different ones attract. In fact,in the magnetic field of the Earth the geographic South and the North pole don’t match with the magnetic ones. THE FIELD LINES Field lines are generated by two poles characterized of direction and verse : • Direction is given by the straight line that links the two poles. • Verse goes from the North to the South Pole . So the field lines: • are bribes to the direction of the field. • get out from the North Pole of the magnets and goes to the South. • their density is directly proportional to the intensity of the field. DIFFERENCES BETWEEN MAGNETIC AND ELETRIC FIELDS THE MAGNETIC FIELD THE ELECTRIC FIELD Because of the magnetization of Instead, in this case, the charges a ferromagnetic object, there go from the first to the second aren’t passages of magnetic corp. poles. The two poles can’t divide. There are isolated positive or negative electric charges . In the second part we are going to show: • The magnetic field generated by a wire crossed by current • The experiences of some of the most important scientists • The flow in a flat surface MAGNETIC FIELD GENERATED BY A WIRE CROSSED BY CURRENT What did Oersted find out? The experience of Oersted shows that a wire crossed by current generate a magnetic field. What did Faraday find out? Instead,thanks to Faraday,we know that this wire crossed by current,in a magnetic field, is subjected to a force. The verse of the magnetic force is given by the right hand rule. Thanks to Oersted and Faraday we know that There’s a relation between electric current and the magnetic field because the electric current: • Generates a magnetic field • Is subjected to a magnetic force. So it is possible that there would be a magnetic force between two wires because each of them has those characteristics. AMPERE He experienced that : • two straight and parallel wires attract each other if they are crossed by a current in the same verse and they repulse if it is opposite. • Between this two wires there’s a magnetic force. The Ampere’s law The force of a wire is directly proportional to the two currents that are circulating but it also indirectly proportional to the distance between the wires. What is an ampere? It’s a fondamental unite of measure of SI. It’s the intensity of electric current in two straight and parallel conductors situated 1 metre to the other in the vacuum. There’s a force of 2x10^7 N. The amperometer is used to measure the intensity of the current and it’s inserted in a circuit where there’s the current we want to measure. What is a coloumb? It’s the charge that goes throught a section of the wire in which there’s the electric charge of 1 ampere. THE INTENSITY OF THE MAGNETIC FIELD As regards the direction and the verse,we use a magnetic needle. For the intensity we use a wire crossed by current in the magnetic field. B=F/il THE MAGNETIC FORCE ON A WIRE CROSSED BY CURRENT Once you’ve known the magnetic field,you can calculate this force. When the wire is perpendicular to the field lines,it is subjected to a force F=Bil It is perpendicular to the magnetic field and the wire. Instead the verse is given by the right hand rule. • When B is perpendicular the magnetic force is maximum. • When B is inclined, B is lower. • When B is parallel to the wire,the magnetic force is zero. THE MAGNETIC FIELD GENERATED BY A WIRE CROSSED BY CURRENT The force that the second wire gives to the first one is equal and opposite. So,two equally orientated wires attract each other. In the other case,the wires repulse. THE MAGNETIC FIELD OF A SPIRE Let’s consider a spire ( a circular conductor wire) crossed by current ; in every point, B is perpendicular. The verse is given by the right hand rule. The intensity by : B= (µ/2) (i/R) THE MAGNETIC FIELD OF A SOLENOID The solenoid is made up of a wire which is wrapped to a propeller. If it is infinitely wide: The outer magnetic field is equal to zero, instead the interior one is uniform and parallel. If it is normal: The interior magnetic field is particularly intense,instead the outer one is weak. In the middle the lines are parallel and equidistant,that’s why the magnetic field is uniform. B=m(Ni/l) Aurora borealis This is a phenomena that occurs near the magnetic poles. It’s the result of collisions between gaseus particles in Earth’s atmosphere with charged particles released from the sun’s atmosphere. The colour is given by the type of gas that are colliding. LORENTZ’S FORCE •Magnetic field is produced by electric charges which are in motion. •These electric charges are subjected to strength due to a magnetic field. Magnetic force works on a moving charge. THE MOTION OF A CHARGE IN A AN UNIFORM MAGNETIC FIELD DK=W=0 (Because of the cinetic energy theory) So the cinetic energy of the charge doesn’t change. The Lorentz’s force can’t change the value of the charge’s velocity. Motion with perpendicular velocity to a uniform field (B) The Force : • Is always perpendicular to velocity • Is perpendicular to B • Has a constant value given by Fq=qvB r=mv/qB The flow in a flat surface F(B)=BS=Bscosa The flow is measured in weber. • It is positive when the lines of the magnetic field come out. Cosa>0 • It is negative when the lines of the magnetic field come in. Cosa<0 The flow in a no-flat surface The surface is divided in n parts. Gauss’ theorem for magnetism In every closed surface it is equal to zero. F(B)=0 Thank you for your attention. Team n.6 : Castelluccio Camilla Foglio Arianna Identi Noemi Lina Marasco Antonio Russo Carmine