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Secondary 4 Combined Science Physics Composition Situational Writing Quiz
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Secondary 4 Combined Science Physics Quiz - Composition Situational Writing
Answer Key and Marking Scheme
Total Marks: 40
Section A: Structured Response (Questions 1–5)
1. State two essential features that should be included in the "Procedure" section of the report. [2]
Answer:
- A clear, numbered sequence of steps describing what was done. [1]
- Specification of apparatus used and how measurements were taken (e.g., "The length of the pendulum was measured from the point of suspension to the centre of the bob using a metre rule"). [1]
Accept any two relevant features such as: variables controlled, how data was recorded, safety precautions, or repeated measurements.
2. Rewrite the statement using more precise scientific language. [2]
Answer: "The ball accelerated because work was done on it, transferring kinetic energy to the ball." [2]
Accept: "A force was applied to the ball, causing it to accelerate and gain kinetic energy." Award [1] for mentioning force or work done; [1] for linking to kinetic energy or acceleration.
3. Identify two weaknesses and explain how it could be improved. [2]
Answer: Weakness 1: The statement "metal is colder than wood" is factually incorrect—both are at room temperature. [1] Weakness 2: The answer does not explain the scientific reason (metal is a better conductor, so it conducts thermal energy away from the hand faster, creating the sensation of coldness). [1]
Award [1] for each correctly identified weakness with explanation.
4. Explain why this description is incomplete and provide a more accurate version. [2]
Answer: The description is incomplete because it does not specify how the particle motion changes or mention changes in particle arrangement/spacing. [1] Improved version: "The particles vibrate more vigorously about their fixed positions as they gain kinetic energy. Eventually, they overcome the attractive forces holding them in place and move more freely, with increased spacing between particles as the solid melts into a liquid." [1]
Award [1] for identifying the incompleteness; [1] for a substantially improved description.
5. Suggest two specific details that should be included in a well-written observation. [2]
Answer:
- The colour and movement pattern of the potassium permanganate as it dissolves and traces the convection current (e.g., "a purple streak rising from the crystal, moving across the surface, then descending"). [1]
- The direction and path of the coloured water relative to the heat source (e.g., "the purple water rises directly above the flame, moves horizontally near the surface, and sinks at the cooler side"). [1]
Accept any two specific, relevant observational details.
Section B: Data Response and Explanation (Questions 6–10)
6. Write a short paragraph describing the trend shown by the data. [2]
Answer: "The temperature of the water decreases over time, from 80°C at 0 minutes to 50°C at 10 minutes. The rate of cooling is not constant: it is faster initially (cooling by 8°C in the first 2 minutes) and gradually slows down (cooling by only 4°C between 8 and 10 minutes). This is because the temperature difference between the water and the surroundings decreases, reducing the rate of thermal energy transfer." [2]
Award [1] for describing the overall trend; [1] for noting the changing rate of cooling with explanation.
7. Rewrite this conclusion to make it scientifically meaningful. [2]
Answer: "The experiment demonstrated the principle of moments. When the clockwise moment (force × perpendicular distance from the pivot) equalled the anticlockwise moment, the rule was in rotational equilibrium and balanced horizontally. This confirms that for an object in equilibrium, the sum of clockwise moments equals the sum of anticlockwise moments about the pivot." [2]
Award [1] for mentioning the principle of moments; [1] for explaining the equilibrium condition.
8. Write a model answer that includes both the working and a clear explanation of each step. [2]
Answer: "To find the acceleration, I use the equation of motion: s = ut + ½at², where s is displacement (100 m), u is initial velocity (0 m/s, since the car starts from rest), t is time (5.0 s), and a is acceleration. Substituting: 100 = (0)(5.0) + ½ × a × (5.0)² 100 = ½ × a × 25 100 = 12.5a a = 100 ÷ 12.5 = 8.0 m/s² Therefore, the car accelerates at 8.0 m/s²." [2]
Award [1] for correct equation and substitution; [1] for clear explanation and correct final answer with units.
9. Critique this extract by identifying two ways it could be improved. [2]
Answer: Improvement 1: The description is vague ("connected the wires"). It should specify the circuit arrangement (series or parallel) and include a circuit diagram or clear description of connections. [1] Improvement 2: The explanation "because there is more resistance" is incomplete. It should explain that adding a second bulb in series increases the total resistance of the circuit, which reduces the current (I = V/R), causing both bulbs to be dimmer. [1]
Accept other valid improvements such as: including measured values of current/brightness, using scientific terminology, or stating the relationship between resistance and current.
10. Explain why this answer would lose marks and provide a corrected version. [2]
Answer: The answer would lose marks because: (1) it uses the word "heat" instead of "thermal energy" or "infrared radiation"; (2) it does not name the process (radiation); (3) it does not explain that radiation can travel through a vacuum without a medium. [1] Corrected version: "Thermal energy from the Sun is transferred to the Earth by radiation, in the form of infrared electromagnetic waves. Unlike conduction and convection, radiation does not require a medium and can travel through the vacuum of space." [1]
Award [1] for identifying at least two weaknesses; [1] for a substantially corrected answer.
Section C: Extended Writing and Application (Questions 11–15)
11. Write a clear, logically sequenced method for determining the density of an irregularly shaped stone. [3]
Answer:
- Measure the mass of the stone using an electronic balance. Record the mass (m) in grams. [1]
- Partially fill a measuring cylinder with water and record the initial volume (V₁) in cm³. Read the bottom of the meniscus at eye level to avoid parallax error. [1]
- Carefully lower the stone into the water using a thread, ensuring it is fully submerged. Record the new volume (V₂).
- Calculate the volume of the stone: V = V₂ - V₁.
- Calculate the density using the formula: ρ = m / V. State the answer in g/cm³. [1]
Award [1] for mass measurement; [1] for volume by displacement with meniscus reading; [1] for calculation and units. Deduct marks for illogical sequence or missing precautions.
12. Rewrite this aim using appropriate scientific language and identify the independent and dependent variables. [2]
Answer: Rewritten aim: "To investigate how the surface area of water exposed to air affects the rate of evaporation." [1] Independent variable: surface area of water exposed. Dependent variable: rate of evaporation (measured by the decrease in mass or volume of water over time). [1]
Award [1] for a clear, scientific aim; [1] for correctly identifying both variables.
13. Write a full-mark model answer explaining why gas pressure increases when temperature is raised. [3]
Answer: "When the temperature of a gas in a sealed container is raised, the gas particles gain kinetic energy and move faster. [1] These faster-moving particles collide with the walls of the container more frequently and with greater force per collision. [1] Since pressure is the force exerted per unit area on the walls, both the increased frequency and force of collisions result in a higher pressure. The volume is constant because the container is sealed, so the particles cannot expand to reduce the pressure." [1]
Award [1] for linking temperature to kinetic energy; [1] for explaining collision frequency/force; [1] for linking to pressure and noting constant volume.
14. Rewrite this evaluation to include specific reference to accuracy, reliability, and suggestions for improvement. [2]
Answer: "The experiment produced results that were reasonably close to the accepted value for the refractive index of glass (1.50), with our average value being 1.47, indicating good accuracy. However, there was some variation between repeated trials (range of 0.05), suggesting that reliability could be improved. [1] To improve the experiment, we could take more repeated readings at each angle of incidence, ensure the ray box is aligned precisely with the protractor, and use a thinner beam of light to locate the refracted ray more accurately. [1]"
Award [1] for addressing accuracy and reliability with specific reference to results; [1] for suggesting at least two relevant improvements.
Section D: Error Analysis and Precision (Questions 15–20)
15. State the precision of the measurement and explain how it should be recorded. [2]
Answer: The precision of a ruler with millimetre markings is ±0.5 mm (or ±0.05 cm). [1] The measurement should be recorded as 15.20 cm (to two decimal places) to reflect that the reading was taken to the nearest 0.05 cm. This shows the uncertainty in the last digit. [1]
Award [1] for stating the precision; [1] for correct recording format with explanation.
16. Explain why this recording is ambiguous and state how it should be written correctly. [1]
Answer: "100 g" is ambiguous because it does not indicate the precision of the measurement (it could mean 100 g exactly, or rounded to the nearest 100 g). It should be written as "100.0 g" if measured to the nearest 0.1 g, or "100.00 g" if measured to the nearest 0.01 g, depending on the balance used. [1]
Award [1] for explaining the ambiguity and providing a corrected format.
17. Comment on the accuracy and precision of this result and suggest how the student should present the final answer. [2]
Answer: Accuracy: The result (343.2145 m/s) is close to the accepted value (340 m/s), with a percentage error of about 0.95%, indicating reasonable accuracy. [1] Precision: The result is stated to 6 significant figures, which is overly precise for the likely experimental method. The student should present the answer to an appropriate number of significant figures (e.g., 343 m/s or 3.4 × 10² m/s) based on the precision of the measurements taken. [1]
Award [1] for commenting on accuracy; [1] for addressing over-precision and suggesting appropriate rounding.
18. Identify three errors or omissions in this answer. [2]
Answer: Error 1: The answer lacks units (should be m/s²). [1] Error 2: The negative sign may be incorrect or unexplained—if the question asks for "magnitude," the answer should be positive (4 m/s²). [1] Error 3: The answer does not show any working or explain how the value was obtained from the graph. [1]
Award [1] for any two correct errors; [2] for all three.
19. Explain why this is insufficient and provide the corrected version. [2]
Answer: The recording is insufficient because it omits the units for both current and voltage. In a scientific report, all measurements must include appropriate SI units. [1] Corrected version: "The current was 0.5 A and the voltage was 3 V." [1]
Award [1] for identifying the missing units; [1] for the corrected version with correct units.
20. Rewrite this description using correct scientific terminology. [1]
Answer: "The image is magnified (or enlarged) and inverted." [1]
Accept: "The image is larger than the object and upside down / inverted." Award [1] for using both "magnified" (or "enlarged") and "inverted."
END OF ANSWER KEY