o It can be magnetized more strongly by stroking it with one end of a magnet o

O it can be magnetized more strongly by stroking it

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o It can be magnetized more strongly by stroking it with one end of a magnet o Most effective method: place it in a solenoid and pass a large, direct current (d.c.) through the coil. Methods of demagnetisation: o If a magnet is hammered, its atomic magnets are thrown out of line and it becomes demagnetized. o Heating a magnet to a high temperature also demagnetize it. o Stroking with another magnet to destroy the alignment of poles o Place magnet with poles opposite to that which is induced by a d.c. current and insert into coil with d.c. current o Most efficient method: place magnet inside a solenoid connected to an alternating current (a.c.) supply. Soft Iron vs. Steel SOFT IRON STEEL Gets magnetized faster but loses its magnetism as soon as inducing magnet is removed. High susceptibility but low retentivity Use: core in the transformer Slow to be magnetized but retains acquired magnetism for a long time. Low susceptibility but high retentivity. Use: making magnets. Permanent Magnet vs. Electromagnet PERMANENT MAGNET ELECTROMAGNET Design: hard magnetic material Use: for applications where magnetism is needed over long periods fridge doors Design: Uses a solenoid to create magnetic field Use: For applications where magnetic field needs to be turned on & off - scrap metal moving
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CIE IGCSE PHYSICS//0625 P AGE 14 OF 21 4.2 Electric Charge There are 2 types of charges: positive and negative. Unlike charges attract and like charges repel. The SI unit of charge is the Coulomb (C). The presence of an electrostatic charge can be detected using a leaf electroscope. o If a charged object is placed near the cap, charges are induced. o The metal cap gets one type of charge (positive or negative) and the metal stem and gold leaf get the other type of charge so they repel each other. Electric field: region in which electric charge experiences a force. The direction of an electric field at a point is the direction of the force on a positive charge at that point Conductors: materials that let electrons pass through them. Metals are the best electrical conductors as they have free electrons. E.g. copper Insulators: materials that hardly conduct at all. Their electrons are tightly held to atoms and hardly move, but they can be transferred by rubbing. E.g. Rubber Simple Field Patterns: Parallel plates Point charge +ve and -ve +ve and +ve Induced charges: o Charging a body involves the addition or removal of electrons. o A charge that “appears” on an uncharged object because of a charged object nearby o For example if a positively charged rod is brought near a small piece of aluminum foil, electrons in foil are pulled towards rod, which leaves the bottom of the foil with a net positive charge.
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