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.
Help!
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| show | magnetic | Means affected by a magnet !
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| show | iron, steel, nickel and cobalt | There are others but they are usually mixtures of several magnetic materials
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| show | magnetic field | Think of "lines of force"
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| The magnetic field of a magnet can be made visible by using . . . | iron filings or plotting compasses | show 🗑
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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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| A bar magnet which is suspended by a thread will eventually . . . | come to rest pointing North-South | show 🗑
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| The Earth has a magnetic field around it which resembles that of a . . . | bar magnet | show 🗑
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| When a coil of wire has an electric current flowing in it, the coil acts like a . . . | bar magnet | show 🗑
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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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| A strong electromagnet needs to have a core made of . . . | soft iron | show 🗑
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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 . . . | alternating current | show 🗑
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| show | reverses the poles | This is what AC does 50 times a second
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| show | circuit breakers ( and relays ) | When a large current flows, the electromagnet attracts an iron bar which opens a switch
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| When a wire carrying an electric current is placed in a magnetic field it may experience a . . . | show | 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 . . . | electric motor | show 🗑
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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 . . . | show | Actually a voltage is induced first and then a current flows in the circuit
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| show | reverse | that is, change from one direction to the opposite direction
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| The production of electricity by means of a coil of wire moving in a magnetic field is called . . . | electromagnetic induction | show 🗑
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| show | transformer | not a 'robot'
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| Transformers are used at power stations to . . . | show | 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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| Electricity supplied by the National Grid is at 400 000 volts. This is too high to use in the home so the voltage must be . . . | reduced by a transformer | show 🗑
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| A generator consists of . . . | show | It produces alternating current
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| A transformer can only work with AC because . . . | it needs a changing magnetic field | show 🗑
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| If a wire or coil moves through a magnetic field we say it is . . . | cutting the lines of force | show 🗑
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| When a wire cuts through a magnetic field . . . | show | A current will flow if we connect the wire to a complete circuit
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| show | increase | 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 . . . | higher than the input voltage | show 🗑
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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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