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SECTION A: ANSWER ALL QUESTIONS
(1a)
=PARALLEL CONNECTION=
(1b)
=SERIES CONNECTION=
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(2a)
Total resistance = R1 + R2 + R3
R(total) = 50 + 100 + 100
R(total) = 250 ohms
(2b)
1/R(total) = 1/R1 + 1/R2 + 1/R3
1/R(total) = 1/50 + 1/100 + 1/100
1/R(total) = 0.02 + 0.01 + 0.01
1/R(total) = 0.04
R(total) = 1 / 0.04
R(total) = 25 ohms
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(3)
(i) A fuse is a safety device that protects circuits by breaking the flow of current during overloads, while a meter is a measuring device used to quantify electrical parameters like current, voltage, or resistance.
(ii) A fuse is a consumable component that needs replacement after operation, while a meter is reusable and designed for repeated use.
(iii) A fuse is installed permanently in circuits to ensure protection, while a meter is portable and used for diagnostic or monitoring purposes.
(iv) A fuse operates automatically to disconnect a circuit, while a meter requires manual operation to take measurements.
(v) A fuse is designed to prevent hazards like fire or damage, while a meter is intended to provide information for analysis and troubleshooting.
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(4a)
Elastomeric polymers are flexible, rubber-like materials that can stretch significantly and return to their original shape after deformation. They are commonly used in products like tires, gaskets, and elastic bands.
(4b)
Elastomeric sealant is a type of flexible sealing material that can stretch and compress to accommodate movement in joints or gaps without cracking. It is often used in construction and automotive applications to seal gaps and prevent leaks.
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(5)
(PICK TWO ONLY)
(i) Ambient lighting
(ii) Task lighting
(iii) Accent lighting
(iv) Decorative lighting
(v) Natural lighting
(vi) Wall lighting
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(6a)
Illumination is the process of lighting a space or area, typically by using artificial or natural light sources, to make it visible or to enhance visibility.
(6b)
Luminance is the measure of the amount of light that is emitted, transmitted, or reflected from a surface in a specific direction, often perceived as brightness by the human eye.
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(7)
Luminance = Reflectance × Illuminance
Reflectance = 60% = 0.60
Illuminance = 200 lux
Luminance = 0.60 × 200
Luminance = 120 cd/m²
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(8a)
Airborne sound refers to sound waves that travel through the air. These sound waves are produced by vibrating objects, and they move through the air to reach the listener’s ear. The propagation of airborne sound is influenced by factors like frequency, air temperature, and humidity.
(8b)
Absorption coefficient is a measure of how much sound is absorbed by a material when sound waves strike its surface. The value ranges from 0 to 1, where 0 means no sound absorption and 1 means complete absorption of sound. Different materials have different absorption coefficients depending on their structure and composition.
(8c)
Reverberation is the persistence of sound in an enclosed space after the original sound source has stopped. It occurs due to multiple reflections of sound waves off walls, ceilings, and other surfaces. Reverberation time is the duration it takes for the sound to decay by 60 decibels after the source has stopped.
(8d)
Sound intensity is the amount of energy a sound wave carries per unit area in a direction perpendicular to that area. It is measured in watts per square meter and determines the loudness of a sound. The higher the intensity, the louder the sound.
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(9)
(PICK FOUR ONLY)
(i) Durability
(ii) Waterproof
(iii) Flexibility
(iv) High tensile strength
(v) Resistance to chemical and environmental factors
(vi) Easy to apply and work with
(vii) Good adhesion to surfaces
(viii) Temperature resistance
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(10)
Drying shrinkage = (Change in length on drying/Measured length) × 1000
Change in length on drying = 45 µm
Change in length on drying = 0.045 mm
Measured length of brick = 215 mm
Drying shrinkage = (0.045/215) × 1000
Drying shrinkage = 0.2093 mm/m
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SECTION B: ANSWER FIVE(5) QUESTIONS ONLY
(11ai)
Relative humidity is the measure of the amount of water vapor present in the air compared to the maximum amount of water vapor that the air can hold at a given temperature. It is expressed as a percentage. A relative humidity of 100% indicates that the air is fully saturated with moisture and cannot hold any more, leading to phenomena such as dew, fog, or precipitation.
(11aii)
The dew point is the temperature at which air becomes saturated with moisture and water vapor begins to condense into liquid water. At this temperature, the relative humidity reaches 100%. The dew point varies with the amount of moisture in the air; higher moisture content results in a higher dew point. When air cools to its dew point, condensation occurs, which can lead to dew formation on surfaces or fog in the atmosphere.
(11b)
Condensation in buildings typically occurs when warm, moist air comes into contact with cooler surfaces that are at or below the dew point temperature. The process typically occurs in the following steps:
(i) Warm Air Containing Moisture: Indoor activities such as cooking, bathing, and drying clothes increase the moisture content in the air. This warm air can hold more moisture than cooler air.
(ii) Cooling of Air: When this warm, moist air moves towards cooler surfaces (e.g., windows, walls), it cools down. As it cools, its capacity to hold moisture decreases.
(iii) Reaching Dew Point: If the temperature of these surfaces is below the dew point of the air, the relative humidity rises. Once it reaches 100%, condensation occurs.
(iv) Visible Condensation: The water vapor condenses into liquid water droplets on these cooler surfaces, which can lead to visible condensation on windows and walls.
Interstitial
(v) Condensation: This type of condensation can also occur within building materials when moisture-laden air diffuses through walls and reaches a cooler area inside the structure, causing hidden dampness that may lead to mold growth and material degradation.
(11c)
To manage and maintain appropriate conditions regarding condensation in buildings, several strategies can be employed:
(i) Adequate Ventilation: Ensuring proper ventilation helps reduce indoor humidity levels by allowing moist air to escape and fresh air to enter. This can be achieved through mechanical ventilation systems or natural ventilation methods like opening windows.
(ii) Insulation: Proper insulation helps maintain surface temperatures above the dew point by minimizing heat loss from warm indoor spaces to colder exterior environments. This reduces the likelihood of surfaces cooling down enough for condensation to occur.
(iii) Humidity Control: Using dehumidifiers or air conditioning systems can help control indoor humidity levels, keeping them within acceptable ranges to prevent condensation.
(iv) Moisture Barriers: Installing vapor barriers in walls and ceilings can prevent moisture-laden air from reaching cooler surfaces within construction materials where condensation could occur.
(v) Regular Maintenance: Regularly checking for leaks and ensuring that building materials are not saturated with moisture will help prevent conditions conducive to condensation.
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(12a)
Density = Mass / Volume
Given:
Mass = 12 tonnes x 1000 kg/tonne = 12,000 kg
Volume = Length x Width x Height = 2.5m x 2m x 1m = 5m³
Density = Mass / Volume = 12,000/5 = 2400
Density = 2400kg/m³
(12b)
(i) Conductors:
Conductors are materials that allow the flow of electric current or heat through them with minimal resistance. This property, known as conductivity, enables free movement of charge carriers, typically electrons or ions, within the material. Common examples of conductors include metals such as copper, aluminum, and silver. These materials are used in electrical wiring and components due to their ability to efficiently transmit electricity.
(ii) Insulators:
Insulators are materials that significantly hinder the flow of electric current or heat. They have high resistance to the movement of charge carriers, meaning that when a charge is applied, it does not distribute throughout the material. Examples of insulators include rubber, glass, and plastic. These materials are commonly used to coat electrical wires and components to prevent unintended current flow and protect users from electric shock.
(iii) Semi-conductors:
Semiconductors are materials that exhibit electrical conductivity between that of conductors and insulators. Their conductivity can be altered by introducing impurities (a process known as doping) or by changing environmental conditions such as temperature. Silicon is a widely used semiconductor in electronic devices. Semiconductors are essential for creating components like diodes, transistors, and integrated circuits, which are foundational to modern electronics.
(iv) Sound Reflection:
Sound reflection refers to the phenomenon where sound waves bounce back after striking a surface. When sound waves encounter a barrier, such as a wall or a hard surface, they can reflect back into the same medium rather than being absorbed or transmitted through it. The angle at which the sound wave strikes the surface (angle of incidence) equals the angle at which it reflects off (angle of reflection). This principle is crucial in various applications such as acoustics in concert halls and the design of soundproofing materials.
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(14a)
(i) Strength: Mortar must have sufficient strength to bond masonry units together and withstand various loads and stresses.
(ii) Water Retention: Good mortar should retain water during application to ensure proper hydration and bonding, preventing premature drying.
(iii) Workability: Mortar should be easy to mix, transport, and apply, allowing for efficient placement without compromising its performance.
(iv) Adhesion: It should develop strong adhesion to the masonry units, ensuring a durable bond that can resist environmental factors.
(v) Durability: Mortar should be resistant to weathering, moisture penetration, and other environmental conditions to maintain structural integrity over time.
(14b)
(i) Dressing Compound:
A dressing compound is a chemical or coating applied to construction materials, such as stone or concrete, to enhance their surface finish, durability, and resistance to stains or weathering. It may also improve the aesthetic appearance of masonry or other surfaces by providing a polished or smooth finish.
(ii) Doweller:
A doweller is a mechanical tool or device used to install dowels small cylindrical rods into construction joints, especially in masonry or concrete. It ensures proper alignment and spacing of dowels, which helps in transferring loads between connected structural elements.
(iii) Dowel Bar:
A dowel bar is a short, cylindrical steel rod inserted into concrete slabs or walls to transfer loads across joints and prevent differential movement. Commonly used in road pavements and construction joints, dowel bars ensure load distribution and provide structural continuity while allowing for controlled movement due to thermal expansion and contraction.
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(15a)
TABULATE
=BULKING TEST=
(i) Purpose: The bulking test is used to determine the bulking (increase in volume) of fine aggregates (usually sand) when they absorb water.
(ii) Procedure: Sand is filled in a graduated cylinder, and water is added to it. The increase in volume of the sand is observed, which is expressed as a percentage increase from its original volume.
(iii) Use: It helps to understand how the sand behaves when wet, which can affect the mix design for concrete or mortar.
=SILT TEST=
(i) Purpose: The silt test is used to determine the silt content in fine aggregates (such as sand). High silt content can affect the strength and durability of concrete.
(ii) Procedure: A sample of sand is mixed with water in a jar, stirred, and allowed to settle for some time. The amount of silt (fine particles) that remains suspended in the water is measured.
(iii) Use: This test helps to ensure that the sand used in construction has an acceptable amount of silt, as excessive silt content can weaken concrete.
(15b)
(i) Pressure Head:
Pressure head refers to the height of a column of fluid (usually water) that can be supported by the pressure within the system. It is a measure of the potential energy of the water due to pressure and is expressed in terms of the equivalent height of a water column (meters or feet). For example, a pressure head of 10 meters means the pressure is sufficient to push water up to a height of 10 meters.
(ii) Water Hammer:
Water hammer is a hydraulic phenomenon that occurs when a fluid in motion is suddenly forced to stop or change direction, usually due to the rapid closure of a valve or a sudden pump shutdown. This causes a pressure surge or shockwave in the pipes, leading to a loud banging noise, vibrations, or even damage to the piping system. Proper installation of air chambers, pressure relief valves, or slow-closing valves can help mitigate water hammer.
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(16)
(i) Thermal conductivity:
Thermal conductivity refers to the ability of a material to conduct heat. It is a physical property that quantifies the rate at which heat flows through a material when there is a temperature difference across it. The higher the thermal conductivity, the better the material is at conducting heat. Materials like metals generally have high thermal conductivity, while insulating materials like rubber or foam have low thermal conductivity.
(ii) Thermal resistivity:
Thermal resistivity is the inverse of thermal conductivity. It refers to the ability of a material to resist the flow of heat. A material with high thermal resistivity is a good thermal insulator, meaning it resists the transfer of heat effectively. In simple terms, it measures how well a material can resist the flow of heat. It is particularly useful in determining the insulating properties of materials.
(iii) Septic tank:
A septic tank is an underground chamber used for the treatment and disposal of wastewater from a household or building. It typically holds wastewater (such as from toilets, sinks, and baths) long enough to allow solid waste to settle at the bottom and for oil and grease to float to the top. The liquid wastewater is then filtered and absorbed by the surrounding soil or flows into a drain field. Septic tanks are commonly used in areas without centralized sewage systems.
(iv) Inspection chamber:
An inspection chamber is a small underground structure that provides access to the drainage or sewage system. It allows for inspection, maintenance, and cleaning of pipes or sewers. Inspection chambers are typically installed at junctions or changes in direction of the sewer or drainage pipes. They help ensure that the system is free from blockages and allow workers to carry out repairs if necessary.
(v) Soakaway:
A soakaway is a system used to manage surface water drainage. It consists of a hole or pit that is filled with gravel or similar material and is designed to allow rainwater or wastewater to slowly seep into the ground. Soakaways are commonly used to prevent water from flooding or pooling on the surface by directing excess water into the soil, where it can be absorbed. They are typically used for managing stormwater runoff or treating wastewater from septic systems.
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(17a)
(i) Reduce Moisture Content: Seasoning reduces the moisture content of timber, typically to below 20%. This is essential to prevent problems such as warping, cracking, and decay.
(ii) Increase Strength and Durability: Properly seasoned timber has improved strength and hardness, making it less susceptible to bending and breaking. This enhances its performance in structural applications.
(iii) Prevent Fungal and Insect Attacks: By lowering the moisture content, seasoned timber becomes less attractive to fungi and insects, reducing the risk of rot and infestations.
(iv) Maintain Size and Shape: Seasoning helps maintain the dimensional stability of timber, preventing shrinkage or expansion that can occur with changes in humidity.
(17b)
(i) Base (Pigment): The base is the solid material that forms the bulk of the paint. It provides opacity, durability, and protection to the painted surface. Common materials include white lead, zinc oxide, and titanium dioxide.
(ii) Vehicle (Binder): The vehicle is a liquid that binds the paint components together and adheres the paint to the surface being painted. It can be made from oils or synthetic resins that provide durability and flexibility.
(iii) Solvent (Thinner): Solvents adjust the viscosity of the paint for easier application. They evaporate during drying, leaving behind a solid film. Common solvents include water for water-based paints and turpentine for oil-based paints.
(iv) Drier: Driers are additives that accelerate the drying process of paint by facilitating the oxidation of the binder. They help ensure a quicker curing time for the paint film.
(v) Colouring Pigments: These are materials added to impart color to the paint. They can also enhance other properties such as opacity and UV resistance.
(17c)
(i) Oil-based Paint
(ii) Water-based Paint (Latex Paint)
(iii) Enamel Paint
(iv) Acrylic Paint
(17d)
(i) Oil-Based Paint: This type of paint uses oil (like linseed oil) as a binder. It dries slowly, allowing it to be smoothed and blended easily. It is durable, resists wear and tear, and is often used for wood, metal, and exterior surfaces. However, it emits strong odors and takes longer to dry.
(ii) Water-Based Paint (Latex Paint): This type of paint uses water as the solvent, making it more environmentally friendly with fewer fumes and faster drying time. It is commonly used for interior walls and ceilings due to its easy application, ease of cleaning, and lower environmental impact. It is less durable than oil-based paints but still provides a good finish for most residential uses.
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