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Physics (GCSE) Revision (Electromagnetism)

Quiz yourself by thinking what should be in each of the black spaces below before clicking on it to display the answer.
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Statement
Response
Comment
A magnet exerts a force on any piece of material which is . . .   show Means affected by a magnet !  
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Magnetic materials include . . .   iron, steel, nickel and cobalt   show
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The region of space around a magnetic which can influence magnetic materials is called a . . .   show Think of "lines of force"  
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The magnetic field of a magnet can be made visible by using . . .   show Sprinkle iron filings or place several small compasses around the magnet  
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show North-seeking pole   We usually just call it the North pole - but this is a simplification  
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show come to rest pointing North-South   The magnet aligns itself with the Earth's magnetic field  
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show bar magnet   It looks similar but this does not mean there is a bar magnet at the centre of the Earth  
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When a coil of wire has an electric current flowing in it, the coil acts like a . . .   show You can plot the field using plotting compasses  
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The magnetic field in an electromagnet can be made stronger by . . .   show or by using more turns of wire  
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show soft iron   which is easy to magnetise and demagnetise  
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If a steel rod is placed inside an electromagnet it will . . .   show only if the coil carries a direct current  
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A magnet can be de-magnetised by placing it inside a coil carrying . . .   show This scrambles the atomic magnets and reduces the magnetic field in the magnet to zero  
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show reverses the poles   This is what AC does 50 times a second  
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Electromagnets are used in devices called . . .   show When a large current flows, the electromagnet attracts an iron bar which opens a switch  
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show force   which throws it out of the field  
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The force on a coil of wire in a magnetic field is the principle of the . . .   show which spins continuously in one direction  
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In a simple dc motor, the device which allows it to spin continuously in one direction is called a . . .   show It reverses the direction of current every half turn  
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If a magnet is moved into a coil of wire which is part of a complete circuit, a current is . . .   induced   show
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If a magnet is moved in and out of a coil, the direction of the induced current will . . .   show that is, change from one direction to the opposite direction  
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show electromagnetic induction   Discovered by Michael Faraday in 1831  
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A device which changes the voltage of an AC supply is called a . . .   show not a 'robot'  
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show increase the voltage of the electricity supply   to reduce energy losses  
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show this reduces energy losses   We don't want to pay for what we don't get  
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show reduced by a transformer   called a 'step-down' transformer  
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show a coil of wire rotating in a magnetic field   It produces alternating current  
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A transformer can only work with AC because . . .   show to induce a voltage in the seconday coil  
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show cutting the lines of force   Think of a cheese wire cutting through cheese  
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When a wire cuts through a magnetic field . . .   a voltage is induced between its ends   show
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If a coil rotating in a magnetic field is spun faster, the voltage induced will . . .   show Obviously !  
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show increase its area or the number of turns   Or make the field stronger  
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An AC generator consists of . . .   show Power stations have several of these going at the same time  
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show slip rings and brushes   This prevents sparks ( or tangled wires )  
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The brushes in a generator or motor are usually made from . . .   show It's a good conductor and it's slippery  
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A transformer works because . . .   an alternating current in the primary coil induces another alternating current in the secondary coil   show
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A transformer needs a soft iron core because . . .   it transfers the magnetic field from the primary to the seconday coil   show
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When an alternating voltage is applied across the primary coil of a transformer . . .   show Input and output are both alternating at the same frequency  
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show Vp / Vs = Np / Ns   This is called the 'turns ratio'  
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If there are more turns of wire on the secondary coil of a transformer than on the primary, the output voltage will be . . .   show This is a 'step-up' voltage transformer  
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show steps down current   Power remains constant  
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For a given rate of transfer of energy (power) the higher the voltage . . .   show This reduces heating of the wire  
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Created by: J Thomson
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