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The earth is a giant magnet Magnetic field lines of force leave the north pole and enter the south pole. What is a magnetic field? Magnetic field The space around a magnet where the forces of attraction and repulsion act is the magnetic field. A magnetic field is made up of lines of force. What are poles? The poles represent the part of a magnetic field where the magnetic forces appear to be concentrated. Magnetic flux patterns Magnetic flux patterns Magnetic? These materials along with certain other alloys are called ferromagnetic materials. Hard or soft material? Iron has stronger induced magnetism. Steel has a weaker induced magnetism. Hard or soft? Hard or soft? Iron is a magnetically soft material. Strong but temporary! Steel is a magnetically hard material. Weak but permanent! Induced magnetism Making magnets Single touch method The end where the stroking pole leaves the bar becomes the opposite pole. Making magnets Double touch method The end where the stroking pole leaves the bar becomes the opposite pole. Making magnets: can a magnet have similar poles at its ends? Consequent poles The end where the stroking pole leaves the bar becomes the opposite pole. The Domain Theory of magnets Magnetic material In demagnetized condition Dipoles in magnetic domains Magnetic material In magnetized condition Domain theory explains: 1. Demagnetization: mechanical vibrations can cause demagnetization 2. Magnetic saturation: strength of a magnet cannot be increased beyond a certain limit. 3. Breaking a magnet: breaking a magnet the broken ends maintain the poles. Magnetic keepers Magnetic effect of current electromagnet To tell the poles: 1. face the coil, trace the direction of current flow, if it is anticlockwise then that is the North pole If it is clockwise then that is the South pole 2.Use right hand grip rule, the thumb points to the N, the end is the S Direction of the magnetic field Grip the wire with your right hand, the field lines will go in the direction of the fingers. Magnetic effect of an electric current Magnetic flux pattern due to a current in a long straight wire, Magnetic effect of an electric current Use the right hand grip rule Magnetic flux pattern due to a current in a short circular coil of wire. Magnetic effect of an electric current Magnetic flux pattern due to a current in a solenoid. Grip the solenoid with the right hand with the fingers in the direction of the current The thumb points to the north pole Direction of the magnetic field Grip the wire with your right hand, the field lines will go in the direction of the fingers. Kicking wire experiment Force on conductor Field due to permanent magnet Field due to current in wire Two fields interact to produce force (motion) Fleming’s left hand rule Used to determine direction of motion of conductor d.c. electric motor Fields interact, coil turns END OF MOTORS… Go back and review….. remember… u can not sleep if u don’t know it. sweet dreams