GCSE Science/Generating electricity answers

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Some thoughts on the questions posed... (perhaps this will become an 'answers' page in due course?)

Q1. Think back to the ideas presented on 'GCSE Science/Induction': Increasing the speed of rotation is like moving the magnet in and out of the coil faster, so the waveform on the oscilloscope will be bigger in relation to the y-axis (larger voltage induced). However, since the rate of rotation is increased, the frequency will also be greater, so the peaks will be closer together, hence correct answer is 'C'.

Q2. Some typical sources of a.c. are the alternator on a car and the generator at a power station. Sources of d.c. include dry cells (commonly known as 'batteries' in the UK), photovoltaic cells (solar panels), lead-acid accumulators and smoothed d.c. power supplies found in science labs.

Q3. A typical device which only works with d.c. is (as mentioned in the article - if you were paying attention!) the electric motor (the split-ring commutator type depicted in the article about the motor effect). A device which doesn't mind whether you use a.c. or d.c. is the light bulb.

Q4. Was this question put in as a red-herring, or a means of challenging brighter pupils?! Well, what did you make of it? Tricky, given the setting? Well, since hair-dryers need to blow out a lot of hot air, their power requirement is fairly large. This means that batteries won't last long enough to be a viable option! With this in mind, the only sensible thing to do is use mains, i.e. alternating current. The heater element doesn't care which way the current is flowing - it just gets hot. This does pose a problem for the motor, though. It can't be the split-ring commutator variety, since it would just vibrate on the spot, get hot, and then die! (Electric motors invariably keep their windings from overheating by drawing in cooler air from outside their housing as they rotate.) So, one of those special a.c. motors mentioned earlier has to be used...

Q5. The useful component he was thinking of is called a 'diode'. Diode circuit symbol.png

(Most diodes are now made from semiconductor materials, but the original diode was called a 'thermionic valve'. From your knowledge of Biology (particularly of the heart) why do you think the term 'valve' is appropriate?)