IAN LANG ELECTRONICS

gcse2a

The second written paper in GCSE concerns itself with applications of electronics rather than just bald theory. Not that you don't need a good grasp of the theory as you'll see in the coming questions. We are eased in gently with this:

GCSE Electronics

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Microphone

Speaker

PRE amp

POWER amp

20

800 mV

1

1

1

0

1

1

1

1

0

0

1

3

This is how these answers are arrived at. Where there's a 1 the segment is shining and where there's a 0 the segment is dark. So:

0

If you are not sure where to go with this remember that your transducers always come at the end and fill those in first. There are two transducers, the microphone and the loudspeaker. You know the loudspeaker is the output and the mic the input so stick them at the right end (follow the arrows).

 

That leaves you with a PRE amplifier and a power amplifier. The clue is in the PRE part- it comes PREvious to the power ampliier. What is the difference? Well, the pre-amplifier is concerned with passing as much voltage along as possible. The power ampliier is concerned with the power (voltage and current) and to pass the maximum power the impedance between the power-amp output and the loudspeaker must be equal: there's another way to remember the sequence.

This question continues with the following:

gcse2b

0

0

0

0

1

1

1

1

In a sly way they are testing your knowledge of binary whilst making it look as though they're doing it for LED segments. Don't let them trip you up. If you can't do binary, read the article on the left by clicking the link.

 

Here comes question 3:

 

 

 

Binary gcse3

6V

2s

Look carefully at the question - they first ask you for the AMPLITUDE of the signal. This is a fancy way of saying "how many volts is it" and the top of the square wave on the graph is 6V (the word "amplitude" comes from the Ancient Greek word for "plentiful" and if you learn that you'll remember the rest).

 

They've given you a present by only giving you one voltage in that list of choices but it's just to lull you into a false sense of security. Remember the examiners are not your friends and if they give you a gift it's to lower your guard to what happens next. What happens next in this case is that they ask for the period of the signal and give you a choice of 1 second, 2 seconds and 10 seconds.  They know you aren't going to fall for 10s, because there's five signals in that time, and so they've set up another pitfall. It's very tempting to put 1s as the answer because that's the time the signal is high (ie 6V) for. That is in fact the mark time. It's low (ie 0V) for 1s as well. That's the space time. The period is the mark time PLUS the space time- 2s.

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