Download Examination Paper for Electrical Fundamentals - Cork Institute of Technology, 2007/08 and more Exams Electrical Engineering in PDF only on Docsity!
CORK INSTITUTE OF TECHNOLOGY
INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ
Semester 2 Examinations 2007/
Electrical Fundamentals
Module Code: ELEC 6004
School: Electrical & Electronic Engineering
Programme Title: Bachelor of Engineering in Electrical Engineering – Stage 1
Programme Code: EELEC_7_Y
External Examiner(s): Mr. M. Hennessy, Prof. E. McQuade Internal Examiner(s): Mr. R. Daly, Mr. N. Mulcahy
Instructions: Answer Two Questions From Each Section All formula for calculations must be shown Use separate answer book for each section
Duration: Two Hours
Sitting: Summer 2008
Requirements for this examination:
Note to Candidates: Please check the Programme Title and the Module Title to ensure that you have received the correct examination paper. If in doubt please contact an Invigilator.
Section A - Please use answer book A
Q1 (a) Sketch the reactance/frequency characteristic of a pure inductor. 5 Marks
(b) A 40 Ω resistor, and a 106.2 μF capacitor are connected in series across a 10 V 50 Hz supply. Calculate (i) the capacitive reactance, (ii) the impedance, (iii) the voltage across each circuit component, (iv) the power factor and the power. 15 Marks
(c) Sketch the phasor diagram for the complete circuit above. 5 Marks
Q2 (a) A milli-ammeter requires 100mV across its terminals to give full-scale deflection with a current of 10mA flowing through the coil. Calculate the resistance required in series with the meter so that the combination of meter plus resistor would give a full-scale deflection for 50 V. 10 Marks
(b) How could the milli-ammeter be converted to an ammeter with a full-scale deflection 5.0A and what value of resistance would be required? 10 Marks
(c) Sketch the circuit in each case. 5 Marks
Q3 (a) List the relative advantages and disadvantages of lead-acid and alkaline cells. 8 marks
(b) A battery of 50 cells is charged through a fixed resistor from a constant 120 V supply. At the beginning of the charge, the e.m.f per cell is 1.9 V and the charging current is 4 A. When charging is almost complete, the e.m.f. per cell has risen to 2.2 V. Each cell has an internal resistance of 0.02 Ω. Calculate the value of the external resistor and the current at the end of the charge. 17 marks
Q6 (a) Explain the essential characteristics of a Zener diode and which characteristic it shares with a conventional silicon rectifier diode. 7 Marks
(b) Calculate for the circuit in Fig. 2: (i) The supply current Is when Vs = 24V and Vs = 20V; 6 Marks (ii) The zener current Iz when Vs = 24V and Vs = 20V. 6 Marks
(c) Calculate the average power dissipated in the Zener diode. 6 Marks
Z 9VD (1W)
V FWBRS Fro m ( V p = 24V, V min =20V)
R S = 180Ω (^) I S I L I Z ElectronicLoad
I S I L = 50mA I Z
Fig. 2
