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274, 5.20. CARBON RESISTORS, Electric Cur, resistors. A carbon resistor is made from powdered carbon mixed with a, factured in values from a fraction of an ohm to several million ohms., binding material, Colour code for carbon resistors. Since a carbon resistor, is physically quite small, it is more convenient to use a colour, code indicating the resistance value than to imprint the numeri-, cal value on the case. In this scheme, there are generally four, colour bands A, B, C and D printed on the body of the resistor, as shown in Fig. 5.13. The first three colour bands (A, B and, C) give the value of the resistance while the fourth band (D) tells about the *tolerane., percentage. The table below shows the colour code for resistance values and colour cod, pund, A BCD, Refer, Fig. 5.13, Exam, tolerance., Solut, The c, The colou, Thus the, Colour Code for Resistance Values, Black, Colour Code for Tolerance, Green, Brown, Blue, + 5%, 9, D Pad aivr, Red, Silvera, 2., 3, Violet, 土 10%, No colour 20%, Orange, 1. 4, Yellow, 4, White, 6., The first two colour bands (A, B) specify the first two digits of the resistance value, and the third colour band (C) gives the number of zeros that follow the first twO, 2002 digits. Suppose the first three colour bands (A, B, C) on the resistor are red, brown., (i) To read the resistance value, we refer to the first three colour bands (A, B and a, 3., orange respectively. Then value of the resistance is 21, 000 Q., Red, Brown, 2., Value = 21,000 2, Orange, 1., %3D, 000, (ii) The fourth band D gives the value of tolerance in percentage. If colour of the fourth 521., band is gold, tolerance is ± 5 per cent and if silver, then tolerance is ± 10 per cent. If, the fourth band is omitted, the tolerance is assumed to be ± 20 per cent., 48, VE, 2 3 4, 10, ROY, Britain, Very Good Wite, 8., reat, 6., Black, Red-, Yellow, Brown, Orange, ber, of Note. In order to remember the colour code, the above sentence may be helpful., Green, Blue, Violet, White, Example 5.25. The colour coded carbon resistors are shown in Fig. 5.19. Find their, resistance values., Solution. Refer to Fig. 5.14 (i). The first colour represents the digit 5. The second colour, represents the digit 6. The third colour represents the digit 4, i.e., four zeros. Therefore, the value, of the resistance is 56000 2. The fourth gold strip indicates ±5% tolerance. Hence, resistance, specification of the resistor is, 學, + 5%, & 00009S, Due to manufacturing variations, the resistance value may not be the same as indicated by colour code. T, a resistor marked 100 2; ± 10% tolerance means that resistance value is between 90 2 and 110 S2.