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BUILDING SCIENCE ANSWERS (TYPE A)
SECTION A: ANSWER ALL QUESTIONS
(1a)
(Draw the diagram)
(1b)
(Draw the diagram)
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(2a)
Acceleration is the rate at which the velocity of a body changes with respect to time when a force is applied. It describes how quickly an object speeds up, slows down, or changes direction.
(2b)
Impulse is the total effect of a force acting on a body over a given period of time. It is equal to the product of the applied force and the time interval during which it acts. Impulse changes the momentum of the body.
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(3)
Cellular glass is a rigid, closed-cell insulating material used mainly for thermal insulation and moisture resistance, while cellular lighting diffuser is a translucent plastic sheet designed to scatter and distribute light evenly in interiors.
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(4a)
Water hammer:
Water hammer is a sudden rise in pressure inside a pipe caused when moving water is forced to stop or change direction quickly, usually due to fast valve closure. This creates a shock wave that produces noise and can damage pipes.
(4b)
Hydraulic mean depth:
Hydraulic mean depth is the ratio of the cross-sectional area of flowing water to the wetted perimeter of the channel or pipe. It is used to determine flow efficiency and resistance in open channels and pipes.
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(5)
(i) Direct Hot Water System:Water is heated in the boiler and delivered directly to taps and appliances. It is simple, quick, and suitable for small buildings, but may carry impurities from the boiler. This system heats water almost immediately and requires less pipework. However, it is less suitable for large-scale installations where a constant supply of hot water is needed.
(ii) Indirect Hot Water System: Water is heated in a separate cylinder via a heat exchanger. It is cleaner, safer, and suitable for large buildings, providing a steady hot water supply. The system allows hot water storage, so supply is available even when the boiler is off. It also reduces the risk of contamination and works well with solar or auxiliary heating systems.
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(6)
(i) Fast heat distribution
(ii) High heat-carrying capacity
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(7a)
Thermal conductivity;
Thermal conductivity is the property of a material that describes its ability to conduct heat. It measures how easily heat energy passes through a material due to a temperature difference.
(7b)
Thermal resistivity;
Thermal resistivity is the property of a material that describes its ability to resist the flow of heat. It indicates how strongly a material opposes heat transfer.
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(8a)
Soot:
Soot is a fine black powder made of carbon particles produced when fuel burns without enough oxygen. It usually settles on surfaces such as chimneys, walls, and heating appliances, and is a sign of incomplete combustion.
(8b)
Smoke:
Smoke is a visible mixture of gases, vapours, and tiny solid particles released when a substance burns. It appears as a grey, white, or black cloud and indicates that the combustion process is not fully complete.
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(9)
(i) Extract ventilation uses fans to expel stale air, creating negative pressure for natural inflow.
(ii) Supply ventilation mechanically delivers fresh air via ducts and fans.
(iii) Balanced ventilation combines supply and extract fans for equal air volumes, maintaining neutral pressure .
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(10)
(i) Insufficient air supply limits oxygen for full oxidation.
(ii) Poor fuel-air mixing leads to localized rich zones.
(iii) Low combustion temperatures prevent breaking molecular bonds .
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SECTION B: ANSWER FIVE(5) QUESTIONS ONLY
(12a)
(i) Plain sawn (through and through): The log is sawn along its length into parallel boards; simple and economical.
(ii) Quarter sawn: The log is first quartered lengthwise and then boards are sawn at right angles to the growth rings; produces stable timber with minimal warping.
(iii) Rift sawn: Boards are cut radially from the log to produce straight grain patterns; highly stable but wasteful.
(12b)
(12c)
(i) Barrow run:
A barrow run is a smooth, inclined surface constructed on a building site to facilitate the movement of materials such as sand, gravel, or concrete using a wheelbarrow. It reduces physical effort, speeds up material transportation, and minimizes spillage. Properly constructed barrow runs improve safety and efficiency on site.
(ii) Barrier effect:
The barrier effect refers to the ability of a material, surface, or structure to prevent or reduce the passage of unwanted elements such as moisture, heat, sound, or pests. Common examples include damp-proof membranes, insulation layers, and solid walls. The barrier effect is essential in protecting the building’s structural integrity, improving comfort, and enhancing durability.
(iii) Barytes:
Barytes, or barium sulfate, is a heavy mineral used in construction, particularly in concrete and cement as a weighting agent. It increases density, improves durability, and enhances resistance to chemical attack and radiation. Barytes is also used in specialized applications like heavy concrete for radiation shielding in hospitals and laboratories.
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(13)
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(14a)
Ring circuit installation: A ring circuit installation is an electrical wiring arrangement in which the live, neutral, and earth conductors leave the distribution board, run through a series of socket outlets, and then return to the same origin, forming a complete loop. This loop allows electrical current to flow from both ends of the circuit, reducing voltage drop and sharing the load between two parallel paths. Because of this load-sharing, smaller cable sizes can safely supply more socket outlets without overheating. Ring circuits are widely used for socket outlets in domestic and commercial buildings because they are economical, efficient, and provide higher current-carrying capacity compared to radial circuits.
(14b)
Diversity factor: Diversity factor is a design principle used in electrical installations to estimate the realistic maximum demand of a system. It is defined as the ratio of the sum of the individual maximum demands of appliances to the maximum demand likely to occur when all appliances are operating together.
In practice, not all electrical appliances operate at full load at the same time. Therefore, applying diversity factor helps reduce the required sizes of cables, switches, circuit breakers, and transformers. This results in a safer, more economical installation because it prevents unnecessary oversizing of equipment while still allowing the system to meet actual operating loads.
(14c)
Factor of safety: Factor of safety refers to the margin provided in the design of structures, machines, or components to ensure they can withstand loads greater than the expected working load. It is calculated as the ratio of the material’s ultimate strength to the actual applied or working load. This safety margin accounts for uncertainties such as manufacturing defects, unexpected overloads, wear and tear, environmental effects, and inaccuracies in material properties. A higher factor of safety ensures reliability and reduces the chances of structural failure, making it an essential principle in engineering, construction, and material selection.
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(15a)
The soundness test checks if Portland cement will retain its volume after setting. A cement paste is placed in a Le Chatelier mould and boiled in water for a few hours. After cooling, the expansion is measured. Small expansion means the cement is sound, while excessive expansion indicates unsound cement that may crack or fail in concrete.
(15b)
(i) To increase the strength of the hardened material, since aggregates provide bulk and structural stability.
(ii) To reduce shrinkage of the binder during setting and drying, minimizing cracks.
(iii) To improve durability by making the resulting material more resistant to wear, weathering, and chemical attack.
(iv) To reduce cost, as aggregates are cheaper than cement or binder and therefore lower the overall material cost.
(15c)
Permeability of concrete refers to its ability to allow water, air, or other fluids to pass through its pores or cracks.
Low permeability indicates a dense, durable concrete that resists moisture and chemical penetration, while high permeability makes concrete more vulnerable to deterioration and corrosion of reinforcement.
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(16)
(PICK ANY TWO)
(i) Generator: A generator works on the principle of electromagnetic induction, which states that a voltage is induced in a conductor when it moves through a magnetic field.
In a generator, a coil of wire is rotated within a magnetic field (or a magnetic field rotates around a stationary coil), causing an electrical current to flow in the coil. This converts mechanical energy into electrical energy.
(ii) Transformer: A transformer works on the principle of mutual induction. When an alternating current flows through the primary coil, it creates a changing magnetic field. This changing magnetic field induces a voltage in the secondary coil, either increasing (step-up) or decreasing (step-down) the voltage depending on the turns ratio.
Transformers transfer electrical energy efficiently without changing its frequency.
(iii) Electric Motor: An electric motor works on the principle that a current-carrying conductor in a magnetic field experiences a force (Lorentz force).
When an electric current passes through the motor coil placed in a magnetic field, a force acts on the coil, causing it to rotate and produce mechanical energy. This converts electrical energy into mechanical energy.
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(17)
(i) Base gusset;
A base gusset is a triangular or plate-like reinforcement fitted at the junction between a column and its base plate or footing. It is used to distribute stresses evenly, reduce bending at the connection, and prevent structural failure at the base. Base gussets are commonly used in steel structures to strengthen connections and improve the stability of columns under heavy loads or lateral forces.
(ii) Base course;
The base course is the first structural layer laid on the subgrade or foundation in road construction, pavements, or masonry walls. It provides uniform support for upper layers, helps in load distribution, and prevents deformation of the surface above. The base course also improves drainage, durability, and overall stability of the structure.
(iii) Barrier effect;
The barrier effect is the property of a material or structural element to prevent or restrict the passage of moisture, heat, sound, or pests through walls, floors, or roofs. Examples include damp-proof membranes, insulation layers, and solid walls. The barrier effect is important for protecting structural integrity, improving comfort, and reducing maintenance costs, as it minimizes water ingress, heat loss, and pest infestation.
(iv) Base tie;
A base tie is a reinforcement or tension member that connects a column, wall, or structure to its foundation. It resists uplift, lateral movement, and overturning forces, ensuring the structure remains stable under various loads. Base ties are particularly important in tall or slender structures, and in areas subject to wind, seismic activity, or uneven loading, as they enhance the overall structural safety and rigidity.
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