Every card in Electricity and magnetism, Year 8: electromagnets and circuits
The whole deck, in order — so you can read it through before your child ever sees it.
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- A magnet made by passing an electric current through a coil of wire
An electromagnet
HintIt only works while the circuit is switched on.
WhyA current in a wire produces a magnetic field. Winding the wire into a coil, usually round an iron core, concentrates the field into a useful magnet.
- Which metal is used for the core of an electromagnet?
Iron
HintIt is magnetic, but loses its magnetism as soon as the current stops.
WhyThe core becomes magnetised by the coil and makes the field far stronger. Iron is chosen because it does not stay magnetised afterwards.
- An electromagnet picks up 5 paper clips. The number of turns on its coil is doubled. Does it now pick up more, fewer or the same number?
More
HintEach loop of wire adds to the field.
WhyEvery turn of the coil carries the current round again and adds its own contribution, so more turns give a stronger magnet.
- Besides adding more turns and using an iron core, what change to the electric circuit makes an electromagnet stronger?
A bigger current
HintThink about what is flowing through the coil.
WhyThe magnetic field is produced by the current, so increasing the current increases the field.
- Why does a scrapyard crane use an electromagnet and not a permanent magnet?
It can be switched off to drop the load
HintThink about what has to happen at the end of the lift.
WhyA permanent magnet strong enough to lift a car could never let go of it. Cutting the current releases the load exactly where it is wanted.
- The component drawn as a long thin line beside a short thick line in a circuit diagram
A cell
HintSeveral of them joined together make a battery.
WhyThe long line is the positive terminal and the short thick line is the negative one. Two or more of the symbols in a row stand for a battery.
- The meter drawn as a circle with the letter A inside it
An ammeter
HintIt is always connected in series, in the loop itself.
WhyIt measures current, in amps. All of the current being measured has to flow through it, which is why it sits in the loop.
- An ammeter reads 0.3 A just before a bulb in a series circuit. What does an ammeter read just after the bulb?
0.3 A
HintAsk whether charge can leave the loop anywhere.
WhyCurrent is a flow of charge, and charge is not used up. What the bulb takes from the circuit is energy, so the current is equal at every point in the loop.
- Which meter measures potential difference?
A voltmeter
HintIt is named after the unit it reads in.
WhyIts symbol is a circle with a V inside. It compares the two sides of a component to find the push across it.
- How is a voltmeter connected to measure the potential difference across a bulb?
In parallel with the bulb
HintUnlike an ammeter, it is not placed in the main loop.
WhyIt needs one lead on each side of the component because it measures a difference between two points. It is added after the main circuit is built.
1★ KS3-PHYS-ELE-0031
2★ KS3-PHYS-ELE-0032
3★ KS3-PHYS-ELE-0033
4★ KS3-PHYS-ELE-0034
5★ KS3-PHYS-ELE-0035
6★ KS3-PHYS-ELE-0036
7★ KS3-PHYS-ELE-0037
8★ KS3-PHYS-ELE-0038
9★ KS3-PHYS-ELE-0039
10★ KS3-PHYS-ELE-0040
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