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B.Tech. Foundation Test (Electronics) / page 1 NATIONAL UNIVERSITY OF SINGAPORE B.Tech. Foundation Test – Electronics Time Allowed: 2 Hours September 2007 Answer all twenty multiple choice questions. Put down your name and answer below. Question Name: Answer (Shade one of the boxes A or B or C or D) 1 A B C D 2 A B C D 3 A B C D 4 A B C D 5 A B C D 6 A B C D 7 A B C D 8 A B C D 9 A B C D 10 A B C D 11 A B C D 12 A B C D 13 A B C D 14 A B C D 15 A B C D 16 A B C D 17 A B C D 18 A B C D 19 A B C D 20 A B C D Mark: B.Tech. Foundation Test (Electronics) / page 2 Q.1 Which of the following is correct? A – The source is a current source. B – The current may flow upward or downward depending on i. C – Both A and B are wrong. D – Both A and B are correct. Q.2 The device is giving power. Which of the following is correct? A – v and i have the same sign. B – v and i have the opposite signs. C – v is positive. D – i is positive. Q.3 What is the phase of the complex sinusoid 6 j 7e j 8t ? A – Between 90 0 and 90 0 . B – Between 90 0 and 180 0 . C – Between 90 0 and 180 0 . D – None of the above. Q.4 What is the frequency of the complex sinusoid 6 j 7e j 8t ? A – Equal to 8 Hz . B – Equal to 8 Hz . C – Equal to 8 rad sec . D – None of the above. Q.5 What is the power of 6 j 7 e j 8t 9 sin 11t ? A – Equal to 6 2 9 2 2 . B – Equal to 6 2 7 2 9 2 2 . C – Not defined as the signal is complex. D – None of the above. Q.6 What is the rms value of 4 cos5t 6 sin 7t ? A – Equal to 0.54 2 0.56 2 . B – Equal to 4 6 . C – Not defined as the signal is not periodic. D – None of the above. B.Tech. Foundation Test (Electronics) / page 3 Q.7 A TV signal booster has a gain of 20 dB. Which of the following is correct? A – The output to input power ratio is 100. B – The output to input voltage ratio is 10. C – Both A and B are wrong. D – Both A and B are correct. Q.8 A filter has a frequency response of 4 j6 f . What is the output if the input is 3 5 cos2 7t ? A – Equal to 4 j6 f 3 5 cos2 7t . B – Equal to 43 j 6 f 5 cos2 7t . C – Equal to 12 5 4 2 42 2 cos 2 7t tan 1 42 4 . D – None of the above. Q.9 A 3 F capacitor is in series with a 4 H inductor. The impedance at 5 rad/sec is A – Equal to j15 j 20 . B – Equal to j 20 j 15 . C – Equal to j 5 . D – None of the above. Q.10 A 3 F capacitor is in series with a 4 H inductor. Which of the following is correct? A – The combined impedance is always positive. B – The combined impedance is always negative. C – The combined impedance may be 0. D – None of the above. Q.11 In a Norton equivalent circuit, the current source is 3A and the resistance is 7 . What is the open circuit voltage? A – Equal to 21 V. B – Equal to 5 V. C – Undefined as there is no voltage source. D – None of the above. Q.12 In a Norton equivalent circuit, the current source is 3A and the resistance is 7 . What is the maximum power that can be drawn? A – Equal to 21 W. B – Equal to 10.5 W. 2 C – Equal to 71.5 W. D – None of the above. B.Tech. Foundation Test (Electronics) / page 4 Q.13 The voltage current relationship of a 2-terminal circuit is v 10 5i . What is the internal resistance in the corresponding equivalent Thevenin circuit? A – May be equal to 5 . B – May be equal to 10 . C – May be equal to 2 . D – None of the above. Q.14 What is the frequency response of the circuit, taking the current as output? A – Equal to R jL . B – Equal to R 1 j 2fL . C – Equal to 1 R j 2fL . D – None of the above. Q.15 The output of a circuit is related to its input by vout 3 2 vin . Which of the following is correct? A – The circuit is not linear. B – Superposition applies. C – Both A and B are wrong. D – Both A and B are correct. Q.16 What is the voltage of A relative to B? A – Equal to 10 V. B – Equal to 20 V. C – Equal to 30 V. D – None of the above. Q.17 What is the impedance of the device? A – Equal to j10 . B – Equal to j 20 . C – Equal to j 20 . D – None of the above. Q.18 The inductor current before closing the switch is A – Equal to 2 . B – Equal to 2 3 . C – Equal to 2 3 . D – None of the above. B.Tech. Foundation Test (Electronics) / page 5 Q.19 The capacitor voltage before closing the switch is A – Equal to 12 . B – Equal to 3 . C – Equal to 18 . D – None of the above. Q.20 Immediately after closing the switch, the inductor voltage has a magnitude A – Equal to 20 . B – Equal to 15 . C – Equal to 10 . D – None of the above.