Examiner s Report March 2014

Size: px

Start display at page:

Download "Examiner s Report March 2014"

Wilfrid Wood
7 years ago
Views:

1 Introduction Examiner s Report March 2014 Level 3 Diploma, Unit 1: Fire Engineering Science Many candidates demonstrated basic knowledge and understanding; just over half of the candidates who sat the examination achieved a Pass grade. Candidates were required to answer six questions from a choice of ten questions. The most popular questions with candidates were question 2 (explaining terms), question 7 (formulae and calculations with reference to nozzle discharge and loss of pressure) and question 10 (thermal expansion). The questions where candidates performed best were questions 2, 8 and 10; candidates performed poorly in questions 6 and 9. Feedback on candidate performance in each of the examination questions follows. Question 1 a) Describe what is meant by the term balanced chemical equation. Write a balanced chemical equation for the reaction of sulphur and oxygen. (8 marks) b) Simple balanced chemical equations have limitations and do not describe several factors that can affect the reaction. Briefly describe these limitations. (12 marks) There were few attempts at this question with even fewer candidates understanding the limitations of simple equations. Very few candidates addressed part b) and a number gave very detailed examples of balanced equations whilst failing to supply the simple example requested, namely:- S + O 2 = SO 2. Question 2 Briefly explain the following terms: i. Exothermic reaction ii. Hydrocarbon iii. Viscosity 1

2 iv. Smothering v. Peroxide vi. Positive pressure vii. Convection viii. Inert gas ix. Friction x. Volute (20 marks) This was a popular question that asked candidates to demonstrate basic understanding across the whole syllabus. Concise statements with simple definitions were sufficient to gain good marks. However, marks were missed by candidates who made no attempt to explain the meaning of several terms or who gave an example but neglected to provide an explanation. Question 3 a) In relation to heat detectors, what is a bi metallic strip and how does it work? b) Explain with the aid of a diagram the operating principles of a rate of rise heat detector, indicating the main parts. (7 marks) c) Draw a diagram of an optical smoke detector (light scatter type) in the fire condition, indicating the main parts. (5 marks) d) Describe how an optical smoke detector (light scatter type) works. e) What are the advantages of using an optical smoke detector (light scatter type)? (2 marks) Candidates who performed well on this question gave good descriptions of bi-metallic strips and showed a good understanding of rate of rise detectors. Accurate descriptions were usually accompanied by the inclusion of clearly labelled diagrams. Many candidates did not understand the rate of rise element in the question and there was confusion on the part of some candidates when describing the different detectors. For example in parts c) and d) beam detectors were drawn and described rather than the light scatter optical type required by the question. 2

3 Question 4 a) With regard to electricity, explain the difference between alternating current (a.c.) and direct current (d.c.) b) With the aid of a diagram, describe the operation of a transformer. (14 marks) Candidates often demonstrated good understanding of alternating current frequency and made comparisons with the one directional flow of direct current. Although clear diagrams and basic explanations achieved a good mark, few candidates were able to explain fully the operation of a transformer. Unfortunately a number of candidates made simple statements to the effect that current is a flow of electricity; this gained few marks. Some poor diagrams (often omitting a core) were often accompanied by confused explanations that revealed a basic lack of understanding. Question 5 State the chemical symbol, the atomic number and briefly describe the properties and any significant hazards of the following elements: i. Potassium ii. Nitrogen iii. Chlorine iv. Hydrogen v. Sodium A small number of candidates knew enough chemistry to achieve full marks with this question. Their knowledge enabled them to cover all four components of this question across the five elements specified. Unfortunately many candidates went off course and gave long descriptions of the elements without identifying any hazards. Atomic numbers were not generally well known and it was clear that many candidates made wild guesses at the numbers as well as the symbols. A surprising number of candidates thought that nitrogen was flammable. 3

4 Question 6 a) Describe laminar flow in gases, including a diagram of the flow in your answer. (10 marks) b) Describe turbulent flow in gases, including a diagram of the flow in your answer. (10 marks) This was the least popular question on the paper and, when it was answered, it was generally not answered well. In summary, laminar flow is uniform, steady and often slow over smooth surfaces. In turbulent flow, random changes of velocity and direction occur within the general flow. Successful candidates provided correct descriptions and accurate diagrams. Unsuccessful candidates often gave full descriptions of flame characteristics and Bunsen burners but provided minimal descriptions of the flow characteristics requested. Question 7 a) State and annotate the following formulae: i. Nozzle discharge ii. Frictional loss b) A pump is delivering water through a 225 metre line of 70 millimetre hose, fitted with a branch with a 12.5 millimetre nozzle working at a nozzle pressure of 4 bars. The frictional factor is i. Calculate the loss of pressure due to friction. ii. Calculate the pressure the pump should generate in order to maintain the nozzle pressure of 4 bars. (12 marks) This was a popular question and it was generally well answered. A common error, even by those who gained good marks, was to omit to state the units at all stages. A number of candidates failed to gain easily available marks by not annotating formulae but merely stating them. The calculation involving output in 7 b) ii was generally completed accurately. However pressure loss was often omitted or calculated incorrectly. 4

5 Question 8 A car has crashed and the front of the vehicle is now hanging over the edge of a bridge with the driver still inside. The pivot point of the car is 2 metres from the front. The loads to be considered which are currently keeping the car in equilibrium are a 400 kilogram engine located 1.5 metres from the front; 50 kilograms of shopping in the rear luggage compartment (or boot ) which is 4 metres from the front; and a driver who weighs 100 kilograms and is 3 metres from the front. a) Neglecting any other loads, draw a diagram and show calculations to demonstrate the car is in equilibrium. (10 marks) b) If a winch could be attached to lift the front of the vehicle, what would be the minimum vertical lifting force needed to maintain the equilibrium if the driver was removed? Show all calculations. (5 marks) c) If the driver was removed, an alternative method of maintaining equilibrium would be to add more mass to the load at the rear of the vehicle. What is the mass that would be required to achieve this, allowing a 25% safety margin? Show all calculations. (5 marks) Full marks were achieved by a small number of candidates, but many failed to provide the force requested in part b), leaving the answer as mass instead. Many candidates began well and gained full marks for part a) but then did not attempt (or failed to complete) the calculations in parts b) and c). Question 9 a) Describe the difference between ionising and non-ionising radiation. (2 marks) b) Identify and describe two types of ionising and two types of non-ionising radiation. (12 marks) c) Materials can respond in three ways to radiant energy. Describe these possible responses. Few candidates attempted this question, with even fewer gaining high marks. Candidates who achieved good marks recognised that X rays and gamma rays are examples of ionising radiation, while light, radio waves and microwaves are types of non-ionising radiation. 5

6 Unfortunately, many candidates thought that the question referred to radioactivity and this led them to provide long (and irrelevant) descriptions of alpha and beta particles as types of ionising radiation. Furthermore this often led them to identify X rays and gamma rays as non-ionising radiation. Sadly, candidates who went down this path gained no marks for their responses. Question 10 a) With reference to thermal expansion in solids, define the following terms: i. Coefficient of linear expansion ii. Homogeneous b) Write down the correct formula and calculate the increase in length of a steel beam metres long, using the following information. i. The temperature of the steel has risen from 17 0 C to 62 0 C. ii. The coefficient of linear expansion of steel is c) Briefly describe the relationship between the following: i. linear thermal expansion ii. superficial (area) thermal expansion iii. cubical thermal expansion d) Which design features are incorporated into the construction of bridges to allow for the thermal expansion of metal elements? (2 marks) This was another popular question and it was generally well answered by those candidates who attempted it. However, few candidates were able to define the term homogeneous. Good marks were gained by candidates who understood the mathematical relationship between length, area and volume. The candidates who performed less well on this question often failed to define the terms and merely attempted the calculations (often omitting the units in their answers). 6

7-5.5. Translate chemical symbols and the chemical formulas of common substances to show the component parts of the substances including:

7-5.5. Translate chemical symbols and the chemical formulas of common substances to show the component parts of the substances including: 7-5.5 Translate chemical symbols and the chemical formulas of common substances to show the component parts of the substances including: NaCl [salt], H 2 O [water], C 6 H 12 O 6 [simple sugar], O 2 [oxygen