MARKING GUIDELINES NATIONAL CERTIFICATE (VOCATIONAL) NQF LEVEL 2 NOVEMBER 2009 This marking guideline consists of 8 pages.
(MARKING GUIDELINES) -2- NC770(E)(O30)V SECTION A QUESTION 1: COMPONENTS AND CIRCUIT DIAGRAMS 1.1 1.1.1 1.1.2 1.1.3 1.1.4 1.1.5 1.1.6 1.1.7 1.1.8 1.1.9 1.1.10 Transformer Polarised capacitor Variable resistor (preset) NPN transistor Fixed resistor Variable resistor PNP transistor Fixed inductor Diode Ammeter (10 x 1) (10) 1.2 How to read a 4-band colour-coded resistor Locate the tolerance band (it is usually gold or silver and is separated from the other bands by a space) Start reading the resistance bands from the one end of the resistor Read the colour of the first band, the second band, and the third band (and obtain their values) Write down the values as follows: 1 st colour, 2 nd colour, number of zeros for the 3 rd colour The 4 th colour (tolerance band) determines the tolerance of the resistor. (5 x 1) (5) 1.3 1.3.1 1.3.2 1.4.1 1.4.2 Voltage Parallel (2 x 1) Potentiometer types Carbon composition Wire-wound (2 x 1) The potentiometer can be adjusted up to a maximum value of 350Ω (1 x 1) (1) 1.5 Inductor types 1.5.1 1.5.2 1.5.3 1.5.4 1.5.5 Air core Ferrite core Iron core Preset Variable (5 x 1) (5) 1.6 5 terminals (1 x 1) (1)
(MARKING GUIDELINES) -3- NC770(E)(O30)V 1.7 380/220 AC 250 VA It is a step-down transformer The primary voltage is 380 volts The secondary voltage is 220 volts The maximum supply power is 250 Volt-Amps (4 x 1) (4) [30] QUESTION 2: CIRCUIT DIAGRAMS 2.1 C 1 = 10 µf C 2 = 20 µf V = 50 V Figure 1 2.1.1 2.1.2 C P = (C 1 x C 2 ) (C 1 + C 2 ) = (10 x 20) (10 + 20) = 200 30 = 6,667 µf (3 x 1) Q T = C P x V = 6.667 x 50 = 333,333 µc (2 x 1) (3) 2.2 Resistors connected in series The resulting total resistance will always be larger than the value of the greater resistance. (2 x 1)
(MARKING GUIDELINES) -4- NC770(E)(O30)V 2.3 R 1 = 20 Ω R 2 = 10 Ω R 3 = 5 Ω 1/R P = (1/R 1 + 1/R 2 + 1/R 3 ) = (1/20 + 1/10 + 1/5) = (1 + 2 + 4) 20 = 7 20 Therefore R P Figure 2 R P = 20 7 = 2,857 Ω (2 x 1) 2.4 2.4.1 2.4.2 2.4.3 2.4.4 T T F T (4 x 1) (4) [15] TOTAL SECTION A: 45
(MARKING GUIDELINES) -5- NC770(E)(O30)V SECTION B: BINARY THEORY AND BASIC COMPUTER COMPONENTS QUESTION 3: BINARY THEORY AND FLIP-FLOPS 3.1 2 196 Remainder 2 98 0 2 49 0 2 24 1 2 12 0 2 6 0 2 3 0 2 1 1 0 1 Table 1 Therefore 196 10 = 11000100 2 (5 x 1) 3.2 2 5 2 4 2 3 2 2 2 1 2 0 1 1 0 0 1 1 1 1 0 + 1 0 0 1 1 1 32 0 0 4 2 1 Table 2 Therefore Sum = 39 10 (5 x 1)
(MARKING GUIDELINES) -6- NC770(E)(O30)V 3.3 BCD Input Output - 8 - - 4 - - 2 - - 1 - Decimal 0 0 0 0 0 0 0 0 1 1 0 0 1 0 2 0 0 1 1 3 0 1 0 0 4 0 1 0 1 5 0 1 1 0 6 0 1 1 1 7 1 0 0 0 8 1 0 0 1 9 Table 3 Decoding from the 8421 BCD Code to Decimal (5 x 1) 3.4 _ 3.4.1 S S J J S Q Q J J S Q Q CK CK CK CK K K Q Q K K R Q Q R _ R Figure 3 IEC Symbol for the JK Flip-Flop (6 x 1) 3.4.2 J K Q Q 0 0 Q n Q n 0 1 0 1 1 0 1 0 1 1 Q n Q n Table 4 Truth Table for the JK Flip-Flop (4 x 1)
(MARKING GUIDELINES) -7- NC770(E)(O30)V 3.5 3.6 3.7 A Decade Counter goes through TEN unique combinations of outputs and then resets as the clock proceeds. (2 x 1) Shift Registers can be constructed as special types of counters used to perform mathematical operations. (2 x 1) Falling Time is that time required for a pulse to drop from 90% to 10% of its maximum. (1 x 1) (1) [30] QUESTION 4: BASIC COMPUTER COMPONENTS 4.1 Secondary Memories 4.2 4.3 Hard disk Compact disk (CD) Digital versatile/video disk (DVD) Flash memory/disk Stiffy or Floppy disk, etc [ANY FOUR] (4 x 1) An interface is a link that connects two devices such as a computer and its peripherals. (2 x 1) Two divisions of primary memory Random access memory (RAM) Read-only memory (ROM) (2 x 1) (4) 4.4 4.4.1 4.4.2 4.4.3 4.4.4 4.4.5 4.4.6 4.4.7 D G A F B C E (7 x 1) (7) [15] TOTAL SECTION B: 45
(MARKING GUIDELINES) -8- NC770(E)(O30)V SECTION C: TRANSDUCERS QUESTION 5: TRANSDUCERS USED IN PROCESS CONTROL 5.1 5.2 Fibre Optic cables are thin, flexible and transparent fibres used to transmit light, especially in telecommunications. (2 x 1) Criteria for selecting a good D/A counter Resolution Accuracy, and Speed. (3 x 1) (3) 5.3 5.4 5.5 A Thermistor is a device that has a resistance that varies with changing temperature. (1 x 1) Physical phenomena that Transducers can sense Level (of liquids) Light Temperature Pressure, etc. [ANY TWO] (2 x 1) Categories of Photodiodes Photosensitive Photoemissive. (2 x 1) TOTAL SECTION C: TOTAL: (1) [10] 10 100