ELECTRONIC AND ELECTRICAL FUNDAMENTALS Section A Attempt all the questions in this section (50 marks) 1. Convert the following numbers. ( a ) Binary to Decimal 11101001 2 ( b ) Hexadecimal to Binary E4 16 ( c ) Decimal to Hexadecimal 215 10 2. Identify the circuit symbols shown in Figure Q2( a ) and Figure Q2( b ). ( a ) Figure Q2( a ) ( b ) Figure Q2( b ) 3. Determine the logic input X and Y for the gates shown in Figure Q3( a ) and Figure Q3( b ) respectively. ( a ) X 1 1 Figure Q3( a ) ( b ) 0 Y 0 Figure Q3( b ) 4. Figure Q4 shows a current carrying conductor placed between magnetic poles. The magnetic flux density is 0·2 Tesla. The conductor experiences a force of 1·2 N when the current is 15 A. N S Figure Q4 ( a ) Determine the length of conductor within the magnetic field. ( b ) State what happens to the force when the current direction is reversed. 5. Referring to Figure Q5, and using the supplied datasheet: V IN 330 ? RED LED L424 HDT Figure Q5 ( a ) state the purpose of the series resistor; ( b ) state the maximum forward current the diode can handle; ( c ) state the typical forward voltage drop; ( d ) determine the maximum value of input voltage that can be safely applied. 6. A generator produces a sinusoidal current represented by the equation i = 12sin ? amperes Determine: ( a ) the maximum value of the current; ( b ) the r.m.s. value of the current; ( c ) the average value of the current; ( d ) the instantaneous value of the current when ? = 30°. 7. With reference to the circuit shown in Figure Q7, in which resistor R 1 is 10 k ? and R V can be varied between 5 k ? and 15 k ? : V 0 100 mV R 1 R V Figure Q7 ( a ) name the circuit configuration; ( b ) determine the output voltage when R V is set to 10 k ? ; ( c ) determine the maximum possible output voltage when the input is 100 mV; ( d ) determine the minimum possible output voltage when the input is 100 mV. 8. With reference to the circuit shown in Figure Q8: 3 ? 2 A 10 ? 18 V 12 V R Figure Q8 ( a ) determine the voltage across the 3 ? resistor; ( b ) determine the current through the 10 ? resistor; ( c ) determine the value of resistor R. ( d ) A fault condition causes the 10 ? resistor to be open circuit. Determine the new value of supply current. 9. For the circuit shown in Figure Q9: A B C Z Figure Q9 ( a ) determine the Boolean expression for output Z; ( b ) draw the truth table for the circuit; ( c ) determine the circuit output Z when a faulty condition causes the output of the invertor to be permanently low (logic 0). [Turn over for Section B on Section B Attempt any TWO questions in this section (50 marks) Each question is worth 25 marks 10. ( a ) State the logic output for the logic gates shown in Figure Q10( a )(i) and Figure Q10( a )(ii). (i) 1 0 Z= 1 Figure Q10( a )(i) (ii) 1 0 Z= 1 Figure Q10( a )(ii) ( b ) Add the following binary numbers. (i) 0101 2 + 0101 2 (ii) 0010 2 + 0101 2 ( c ) Draw the logic circuit for the expression Z = A.B + A ¯ .C ( d ) Determine the logic expression for the logic circuit shown in Figure Q10( d ). A Z= B A C = 1 & = 1 Figure Q10( d 10. (continued) ( ) Figure Q10( )(i) shows a logic circuit. 1 R S T 4 2 5 Z= 3 Figure Q10( )(i) (i) Determine the logic expression for the circuit. (ii) Draw the truth table for the circuit. (iii) The circuit shown in Figure Q10( )(i) has developed a fault, and upon testing the outputs shown in the truth table Figure Q10( )(iii) were obtained. Explain which gate (input or output) is at fault and state the nature of the fault. R S T Z 0 0 0 1 0 0 1 1 0 1 0 1 0 1 1 0 1 0 0 1 1 0 1 1 1 1 0 0 1 1 1 0 Figure Q10( )(iii) 11. ( a ) For the circuit shown in Figure Q11( a ), determine: R 1 1 A 8A V S 2 A 20 A R 3 R 5 R 6 R 7 R 4 R 2 Figure Q11( a ) (i) the current flowing in R 3 ; (ii) the current flowing in R 6 . ( b ) For the circuit shown in Figure Q11( b ), determine: R 1 1 A 10 ? 20 ? 10 ? 20 ? V S 4 A 3 A R 3 R 5 R 6 R 7 R 4 R 2 Figure Q11( b ) (i) the voltage drop across R 7 ; (ii) the supply voltage; (iii) the power dissipated in R 7 ; (iv) the energy consumed in 3 hours by the branch containing R 2 & R 4 . ( c ) A variable speed, 10 kW generator produces an output voltage of 120 V, has a flux density of 40 milliTesla, and a conductor length of 25 m. Calculate: (i) the speed of the generator; (ii) the speed of the generator when the output voltage is 200 V; (iii) the maximum current the generator can supply when the output is 200 V. ( d ) A conductor is forced to move downwards within a magnetic field, as shown in Figure Q11( d ). N S Figure Q11( d ) (i) State the formula used to calculate the current in the conductor. (ii) Explain how the direction of the current can be determined. 12. ( a ) For the circuits shown in Figures Q12( a )(i) and (ii) the input voltage is 12 V pk“pk , 50 Hz in each circuit. (i) Assuming that the switch remains open, sketch the input and output waveforms for the circuit shown in Figure 12( a )(i), clearly indicating the differences between the input waveform and the output waveform. D1 C1 V OUT 12 V pk“pk R L Figure Q12( a )(i) (ii) Sketch the output waveform for the circuit shown in Figure 12( a )(ii), clearly indicating the differences between the new output waveform and the output waveform of Figure Q12( a )(i). D1 12 V pk“pk D4 R L D2 D3 Figure Q12( a )(ii) 12. (continued) ( b ) For the circuit shown in Figure Q12( b ): R v R i V IN = 2 V pk“pk R f =100 K V OUT 5 Circuit Gain = -5 1 Figure Q12( b ) (i) state the circuit configuration; (ii) determine the output voltage; (iii) determine the value of R i ; (iv) explain the purpose of R v . ( c ) (i) Identify the circuit shown in Figure Q12( c ). (ii) With reference to Figure Q12( c ), identify the purpose of each of the following components: R 1 & R 2 , C 2 & C 3 . R 1 Ideal Transistor Gain = 500 R 3 C 2 1K5 I C R 2 R 4 C 3 6K8 1·4 V 6 V 0 V V CC 12 V C 1 Figure Q12( c ) (iii) Calculate the output voltage for the circuit shown in Figure Q12( c ) when the input voltage is 20 mV pk“pk . [Turn over for Question 12(c) continued on 12. ( c ) (continued) (iv) When the input voltage is increased to 40 mV pk“pk the output waveform is as shown in Figure Q12( c )(iv). V OUT +6 V -6 V 0 V t (secs) Figure Q12( c )(iv) Explain why the shape of the waveform is non-sinusoidal. (v) Suggest two ways of preventing this.