Magnetism

Het this is Vedika Agrawal
the topic covers magnetism keeping in mind students of physiotherapy for there subject elecrotherapy.
Well it covers magnet of class 10th and 12th and also college level to some extent.
the ppt includes diagrams for almost everything for better visual understanding.
hope you find it helpfull and elaborative.

1. Topic - MAGNETISM PREPARED BY – VEDIKA AGRAWAL (BATCH 2019-20) ROLL NUMBER – 98 GUIDED AND MOTIVATED BY – NIKETA MA’AM MGM ALLIED HEALTH SCIENCE INSTITUTE (MAHSI), INDORE, M.P.

2. WHAT IS A MAGNET ? A magnet is an object which exhibits certain properties: Setting in a north- south direction when suspended freely. Like magnetic poles repel each other and unlike pole attract each other. Produce magnetism in certain substances like nickel, cobalt, steel and iron. Attraction of suitable material . It has magnetic field to which its force is exerted.

3. MAGNETIC LINES OF FORCE It is graphical representation of a magnetic field, which is hypothetical to explain the magnetic phenomenon. It is a smooth curve in order to take shortest path and repel one another i.e. the two lines do not intersect. The lines travels from north to south direction. Tangent at any point in this field will give us direction of magnetic field at that point. They travel most easily through some materials like metals. The path is traced with the help of iron fillings. The field between two unlike poles is concentrated more in between the two magnets.

4. TYPES OF MAGNETS They are of two types: Natural and Artificial Natural magnets are obtained in form of ore. They are weak and shapeless. Artificial Magnets are manmade. They are strong and of different shapes. They are of two types: Temporary Magnets: Magnetism of these magnets is temporary. It is made of soft iron. There is little friction between the molecules. Thus, magnetism is lost very easily. They can be also be easily influenced into orderly pattern. Permanent Magnets: These magnets are permanent. They are made up of nickel, steel and cobalt. The friction between the molecules is great and thus ordered magnetic effect is retained. The heating or banging will disrupt the order and so magnetism of any kind of magnet can be lost.

5. MAGNETIC INDUCTION It is the phenomenon by which magnetism is produced in the magnetic substance with help of magnet. When the poles of powerful magnet is bought closer to a soft iron bar, the bar turns into a magnet. This is because the end of the bar closer to the magnet, becomes unlike pole. Due to this all the opposite poles of the molecular magnet are attracted towards it. This inturn make a magnetic substance turn into a magnet. Magnetic effect is produced by the influence of the magnet over the molecular magnet of the susceptible material. The magnet can even reduce magnetic effect in an object without contact between them.

6. ELECTRO-MAGNETISM It consists of a coil of wire wound onto a soft iron bar. When a current passes through the wire it magnetizes the bar by induction. As soon as the current is put off, the magnetic effect is lost. A current carrying straight wire produces a uniform magnetic field in form of concentric circles along the centre of the coil. The uniformity of field is used as advantage of SWD. The direction of line of force are given by Maxwell Corkscrew Rule and Right Hand Thumb Rule. Maxwell Corkscrew Rule: If a corkscrew is turned indirection of current, along the wire, then the direction in which the thumb rotates is the direction of the magnetic lines of force. Right Hand Thumb Rule: If current carrying wire is to held in you right hand, when the thumb us is pointing in direction of electric current. The direction in which the finger curls gives the direction of lines of force.

7. ELECTRO-MAGNETIC INDUCTION It is Production of electricity from magnetism. It is done through establishment of an EMF in a conductor, when there is relative motion between the conductor (coil of wire) and magnet. The current produced is called induced current. When and electromagnet (a coil of wire carrying current) is kept close to another conductor, it also produces an induced current in the second conductor

8. FARADAY’s WORK IN EMI Whenever magnetic flux is linked with circuit changes, an emf is induced in the circuit For production of EMI three things are required i.e. conductor, magnet and relative motion between two. Faraday stated three laws : Whenever magnetic flux linked with a circuit changes, an EMF is induced in it. An induced EMF exists in the circuit, so long as the changes in magnetic flux are continued. An induced EMF is directly proportional to the negative rate of change of magnetic flux linked with the circuit.

9. LENZ’s AND FLEMING’s LAWS The direction of induced current is determined by Lenz’s and Fleming’s law. LENZ’s LAW states that the direction of induced EMF (current) is such that it opposes the very cause, which provides it. FLEMING’s LAW states that if thumb, index finger, and middle finger of right hand are stretched perpendicularly, then thumb indicates direction of motion, index finger indicates direction of magnetic field and middle finger will indicate the direction of induced current.

10. INDUCTION It is of two types mutual and self inductance Mutual inductance occurs when EMF is induced in adjacent conductor by the magnetic field set up around coil of wire carrying varying current. Self inductance occurs when coil is carrying a varying current. As current increases, the magnetic lines of force moves out, crossing the adjacent turns of wire and thus inducing an EMF in them. According to Lenz law, the induced EMF is in opposite direction to the main current and so opposes the rise. Self induced EMF is thus called back EMF.

11. EDDY CURRENTS Any conductor lying in a varying magnetic field has a EMF induced in it. If conductor is solid, the magnetic lines of force passing through it set up circular currents called eddy currents. These are perpendicular to magnetic lines of force. They produce heating effect and thus are wasteful in many apparatus. It is prevented by laminating the conductor. In physiotherapy they are useful as heat is used to produce heating effect in patients tissues (in SWD).