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CORK INSTITUTE OF TECHNOLOGY
INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ
Semester 1 Examinations 2010/
School: ELECTRICAL & ELECTRONIC ENGINEERING
Programme Title: Bachelor of Engineering – Electronics, Year 1 Bachelor of Engineering (Hons) – Electronic Systems Engineering, Year 1
Programme Code: CR_EELXE_7_Y CR_EELES_8_Y
Module Title: Electrical Science and Circuits 1
Module Code: ELTR
External Examiner(s): Dr Andrew Donnellan Mr Ian Kennedy Internal Examiner: Mr Michael Murray
Instructions: Answer question 1 and three other questions
Duration: 2 Hours
Sitting: Winter 2010
Requirements for this examination:
Note to Candidates: Please check the Programme Title and the Module Title to ensure that you are attempting the correct examination. If in doubt please contact an Invigilator.
Q1. (a) Briefly describe the structure of an atom and how the valence shell
influences atomic properties. [5 marks]
(b) Calculate the value of voltage in Figure 1. [5 marks]
Figure 1
(c) Describe the operation of a Light Emitting Diode commenting on the advantages. [5 marks]
(d) For Figure 2, calculate the currents in each branch of the circuit (I1, I2 and I3) and the voltage at the node (Vc). [20 marks]
(e) For Figure 2, describe with the aid of a diagram how the current I1 and the voltage Vc could be measured using a digital multimeter. [5 marks]
Figure 2
0
5
10
15
20
0 1 2 3
Current (A)
Resistance(kΩ)
(c) Calculate the supply current if (i) R5 is open-circuited and (ii) R4 is short-circuit. [4 marks]
Figure 3
Q5. (a) Describe three ways in which heat energy is transferred, include examples. Describe briefly how heat is removed from the engine in a car. [ 8 marks]
(b) A 2kW electric kettle is used to heat 1 litre of water from a temperature of 15 ºC to 100ºC. Calculate (i) The energy required for this temperature increase and (ii) The time taken for the water to reach 100ºC. (The specific heat capacity of water is 4180 J/kg/K. Water has a density of 1kg/litre) [6 marks]
(c) In reality, the kettle took 30 seconds longer to boil. (i) Calculate the efficiency of the kettle and comment on the possible causes of inefficiency. (ii) Calculate the cost of this inefficiency if the kettle is boiled 10 times each day. (Unit cost of electricity is €0.16/kWh ) [6 marks]
