Engineering - Exam Papers - HL - Paper - 1991
300 Marks
Answer Question 1, Sections A and B and FOUR other questions.
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1.
(100 Marks)
Section A - 50 Marks
Give brief answers to any ten of the following :
| (a) | List the main ways in which toxic materials may present a threat to the person. | |
| (b) | State two main factors in choosing a process to extract a metal from its ore. | |
| (c) | Why does slip occur more easily in structures that are close packed. | |
| (d) | Compare the safety effects of a fuse and a circuit breaker. | |
| (e) | Identify the processes used to manufacture | |
| (i) | porous metal bearings; | |
| (ii) | plastic bottle caps and | |
| (iii) | engine cylinder heads. | |
| (f) | Why should copper pipes not be connected to a galvenised storage tank? | |
| (g) | State two factors which influence the choice of joining process for a particular application. | |
| (h) | Why do metallic structures not shatter like ionic structures when subjected to shock or compressive loads? | |
| (i) | What is a factor of safety? | |
| (j) | What contribution did any one of the following make to technology: | |
| (i) | Ted Hoff or | |
| (ii) | William Shockley or | |
| (iii) | John Fleming. | |
| (k) | Distinguish between primary and secondary memory. | |
| (l) | Identify the pneumatic symbols (i) and (ii) shown. | |
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| (m) | State two advantages of using Computer-Aided Design. | |
Section B - 50 Marks
Answer all of the following :
| (n) | State two main functions
of a transistor. Explain what the letters B and F represent in the transistor specification: BF194. |
| (o) | Identify the transistors represented
by the symbols A and B as shown. Distinguish between the two types of bipolar transistor and explain how they differ. |
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| (p) | An npn transistor is shown in the
diagram. Identify the terminals 1, 2 and 3. What is forward bias and to which junction does it apply? |
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| (q) | Why is silicon preferred to germanium
as transistor material? What are the advantages of transistors over other types of electrical switch? |
| (r) | How is the gain of a transistor
defined? Sketch graphs showing two transistor characteristics. |
2.
(50 Marks)
| (a) | What factors give effect to fracture
in metals? Distinguish between |
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| (i) | brittle fracture and | ||||||||
| (ii) | ductile fracture. | ||||||||
| (b) | Compare the important features of the Izod and Charpy impact tests. A Charpy impact test on a steel specimen gave the following results at different temperatures. | ||||||||
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| Is the steel becoming more brittle or more ductile, as the temperature falls? Interpret your answer. | |||||||||
| (c) | Describe any two of the following tests and state the type of defect for which they are most useful: | ||||||||
| (i) | radiography test; | ||||||||
| (ii) | eddy current test; | ||||||||
| (iii) | liquid penetrant test. | ||||||||
3.
(50 Marks)
| (a) | Identify the microstructures
of carbon steel marked A, B, C and D
as shown. Relate each microstructure to one of the numbered positions on the given equilibrium diagram. |
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| (b) | Differentiate between: | |
| (i) | annealing and normalising; | |
| (ii) | induction hardening and pack carburising. | |
| (c) | Name three elements,
other than carbon, added to steel to produce alloy
steels. What is the effect of each element mentioned on the properties of steel? |
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4.
(50 Marks)
| (a) | State two factors which
affect the solubility of one metal in another. Describe, with the aid of diagrams: |
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| (i) | a dislocation; | |
| (ii) | a vacancy; | |
| (iii) | a substitutional alloy; | |
| (b) | Label the cadmium-zinc diagram fully in your answer book and discuss its main features. | |
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| (c) | For the alloy with 30% cadmium, use the diagram to: | |
| (i) | explain the solidification process from 400°C; | |
| (ii) | estimate the ratio of solid to liquid at 310°C. | |
5.
(50 Marks)
| (a) | What are the essential requirements
of a heat source for welding? State two different heat sources used in welding and explain how the necessary heat is produced in each case. |
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| (b) | Differentiate clearly between: | |
| (i) | the two types oxy-acetylene flame which are reducing in nature; | |
| (ii) | arc welding and resistance welding. | |
| (c) | Explain, with the aid of a diagram, the main features of any arc welding process which uses non-consumable electrodes. | |
OR |
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| (c) | What are the advantages of using
robots in computer aided manufacture? Give three applications of robots in industry. |
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6.
(50 Marks)
| (a) | Describe the basic differences between polyethylene and phenolformaldehyde under the following headings: | |
| (i) | polymerisation process; | |
| (ii) | type of bonding; | |
| (iii) | structure; | |
| (iv) | properties. | |
| (b) | Explain any three of the terms: amorphous; macromolecule; glass transition temperature; vulcanisation. | |
| (c) | Differentiate between the moulding and extrusion of plastics. Comment on the type of product produced in each case, giving appropriate examples. | |
7.
(50 Marks)
| (a) | What factors influence metal removal
rates in a machining process? Determine the metal removal rate in mm3/min, when using a centre lathe, given that: cutting speed = 70 m/min; depth of cut = 3 mm; feed = 0.3 mm/rev. |
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| (b) | Describe the effects on cutting force and power consumption of | |
| (i) | tool geometry | |
| (ii) | cutting speed and | |
| (iii) | depth of cut. | |
| (c) | Explain, briefly, with reference to metrology, any three of the following terms: | |
| (i) | sine bar; | |
| (ii) | slip gauges; | |
| (iii) | precision balls; | |
| (iv) | mechanical comparator; | |
| (v) | optical projector. | |
OR |
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| (c) | What are the essential features of
computer numerical control (CNC)? Indicate the code used to represent any four of the following CNC machining functions: |
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| (i) | linear interpolation; | |
| (ii) | continuation code; | |
| (iii) | start spindle forward; | |
| (iv) | rapid traverse; | |
| (v) | tool change; | |
| (vi) | canned cycle. | |
8.
(50 Marks)
| (a) | Identify the means by which any three of the following are achieved: | |
| (i) | to apply torque to a transmission system; | |
| (ii) | to control the speed of a pneumatic piston; | |
| (iii) | to convert chemical energy directly into electrical energy; | |
| (iv) | to transmit and receive sound waves electrically; | |
| (v) | to switch electronic circuits by light energy. | |
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| (b) | Explain clearly any two of the following: - thermocouple; - strain gauge; - thermistor |
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| (c) | Explain how the pneumatic circuit shown in the diagram operates. Give an application of such a circuit. | |
OR |
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| (c) | Explain how a particular machine tool slide may be operated automatically. | |