10 These tolerances may seem to reflect poor manufacture but in most circuits they are, in fact, quite satisfactory. Relaxing the tolerance enables the makerto sell them more cheaply.

Task 2 Find the values and tolerances of resistors banded as follows. Then compare

your answers with your partner.

_{чптг ь}

1	red	violet	orange	silver
2	blue	grey	brown	gold
3	green	blue	red	silver
4	red	red	green	—
5	brown	black	orange	—
6	orange	orange	brown	gold
7	yellow	orange	red	gold
8	brown	green	green	—
9	violet	green	brown	red
10	white	brown	red	red

Task3

Read this additional text. Answer the questions below, which refer to both texts.

Preferred values

If the maker tried to produce and sell every value of resistance that exists, there would be chaos and the costs would be greatly increased. The actual values made, 5 therefore, are limited to a range called the preferred values. These are listed in the table.

The values may seem illogical at first sight, but this is not so. They stem from the fact 10 that the tolerance extremes of a value reach the extremes of adjacent values, thereby covering the whole range without overlap. Values normally available stop in the megohm decade.

Tolerance
±5%	±10%	±20%
1.0	1.0	1.0
1.1
1.2	1.2
1.5	1.5	1.5
1.6
1.8	1.8
2.0
2.2	2.2	2.2
2.4
2.7	2.7
3.0
3.3	3.3	3.3
3.6
3.9	3.9
4.3
4.7	4.7	4.7
5.1
5.6	5.6
6.2
6.8	6.8	6.8
7.5
8.2
9.1

1. Why are resistors coded with coloured bands rather than some other form of marking?

2. What would be the effect of making resistors with a much higher tolerance?

3. Between which values might a resistor marked green, blue, orange, and silver vary?

4. Why do manufacturers make resistors in the preferred values shown rather than in equally stepped values?

Technical reading Capacitor values

Task 4

Use the following information to name the colour bandings of the capacitors below. (Note: InF = lOOOpF). For example:

220pF, 2.5%

Band I red - 2 Band 3 brown = one zero Band 2 red = 2 Band 4 orange = 2.5% tolerance

band 1 (1st digit)

band 3 (multiplier)

band 5 (voltage)

band 2 (2nd digit)

band 4 (tolerance)

C280 capacitor colour coding. The first three bands give the value (in pF) using the same system as for the four band resistor coding.

		band
		4	5
	black	20%
	white	10%
colour	green	5%
	orange	2.5%
	red	2%	250V
	brown	1%
	yellow		400V

1. lOOpF, 20%

2. 180pF, 10%

3. 22nF, 5% 250V

4. 47nF, 20%

Technical reading Diode codes

Task 5 Identify these diodes with the help of the text below.

1 BAX16 2 BY126 3 BZX55C2V4 4 AA119 5 BPX65

Diode coding

The European system for classifying semiconductor diodes involves an alphanumeric code which employs eithertwo letters and three figures (general purpose diodes) or three letters and two figures (special purpose diodes). The first two letters have the following 5 significance:

First letter - semiconductor material:

A germanium В silicon

С gallium arsenide etc. Ю D photodiodes etc.

Second letter - application:

A general purpose diode

В tuning (varicap) diode

E tunnel diode 15 P photovoltaic diode

Q light-emitting diode

T controlled rectifier