LESSON 3: Electronic Products – Year 10 R.Winter 2009

Things you should buy…A USB memory stick for bringing in files and work –

More reliable than e-mail! – particularly useful when we get onto coursework

A calculator (ideally Scientific)

Lonsdale –GCSE Electronic products – David McHugh ISBN -978-1-905129-11-9

Nelson Thornes -AQA Design and Technology Electronic Products – ISBN 978-1-4085-0417-8

Learning AimsTo understand what S.I units are and how to use and

interpret them

To understand what ohm’s law is and how to use it in voltage, current and resistance calculations

To FINISH creating your PCB layout of a 555 timer board by the end of today’s lesson – including component labels and strain relief holes

To have printed off both a wiring diagram AND a PCB ‘real world’ view of your PCB to help you with construction next lesson.

S.I Units:In science, Engineering, Maths and Electronics, we often

deal with really BIG and really SMALL numbers that would take AGES to write down because they have so many zeros!

Hence a system has been invented known as S.I units (standing for ‘System Internationale d’unites’.... (Invented by the French clearly...) Or in English “international system of units”

Unfortunatly, you Guys and Girls will need to understand how to interpret them as part of your course.....

On the plus side, if you can work with these, then this is pretty much as hard as the Math gets on this course!

How does it work?Basically, large numbers of extra zero’s (either

before or after the decimal point) have an abbreviation in the form of a ‘name’, or a word, or a symbol.

For example “Kilo-Gram”: – the word Kilo actually means ‘one thousand’. Therefore, in numbers, 1 Kilo-Gram is actually the same as 1000 grams.... Hence, 1 Kilo-meter is 1000 meters..... Make sense so far?

To make things harder, there are a whole load of different names, with different symbols that all stand for certain amounts of ‘zeroes’ either before or after a decimal point......

Table of S.I units and there meanings:

Some questions....Convert the following into their ‘long’ form

(write out all the zeros)

a) 1 K-Gramsb) 2.5 G-Hertzc) 256 M-Bytesd)500 m – Amps (watch the ‘lower case’!)e)100 u-Fahradsf)10 n-Seconds

a)= 1000 Gramsb)=2500000000 Hertz c)= 256000000 Bytesd)0.5 Ampse)0.000256f) 0.0000001 Fahradsg)0.0000000 Seconds

Ohm’s Law:Some clever, old and now dead bloke called Charles

Ohm did a lot of the early experiments with Electricity and he came up with a clever formula that linked VOLTAGE, CURRENT and RESISTANCE.

It was clever, because it showed that if you knew any 2 of the above variables, you could always work out the 3rd.

This formula is now known as OHM’S LAW and is very useful in electronics.

Ohms Law:If you write it out, its most common form is:

V= I*R (where V=Voltage, I=Current and R=Resistance)

A more common (and easier way of rembering it) is to use a formula triangle:

How to use the MAGIC triangle....Cover up the ‘value’ you want to

calculate, and you are left with the formula you need to apply.

E.G – if you want to find out current, cover it up and you are left with V ‘over’ R or V ‘divided by’R ....

Hence I = V/R

Hence, if you knew the voltage and resistance of this circuit, you could work out the current flowing....

Quick ‘Formula Triangle’ Questions:Q1)What is the formula for

working out voltage from ohm’s law?

Q2)What is the formula for working out CURRENT from ohm’s law?

Q3)What is the formula for working out RESISTANCE from ohm’s law?

V=IR

I=V/R

R=V/I

Questions:Q1): The power supply in a simple circuit is 9 Volts, and the current that an L.E.D draws is 20 mA. – What value resistor would you need to connect in the circuit to protect it from this voltage?

Q2): A circuit has a total resistance of 2K-ohms and a current of 400 – mAmps is flowing. – What voltage is the circuit at?

Q3): A circuit has a 200-K Volt potential difference, and a total resistance of 20 M ohms. – What is the current flowing in this circuit?

= 450 Ohms

= 800 Volts

=0.01 Amps