📚 Year 10 CCEA Engineering Mock Paper Analysis | Year 10 CCEA 工程单元测试模拟卷解析
This article provides a detailed walkthrough of a mock unit test designed for Year 10 CCEA Engineering students. Each question targets a core topic from the specification, and the paired explanations in English and Chinese will help you consolidate your knowledge and sharpen your exam skills.
本文为 Year 10 CCEA 工程学生设计了一份单元模拟测试，并进行了详细解析。每道题目紧扣考纲核心，配以中英双语深度讲解，助你巩固知识、提升应试技巧。
1. Material Selection for a Lightweight Structure | 轻量化结构的材料选择
The question asked: "An engineer must choose a material for a portable pedestrian bridge that must be light yet strong enough to carry a group of people. Compare aluminium alloy and mild steel, then recommend the best material with justification."
题目问到："工程师需为一座便携人行桥选材，要求轻便且能承载人群。比较铝合金与低碳钢，然后推荐最佳材料并说明理由。"
Aluminium alloy has a density of approximately 2700 kg/m³ while mild steel is about 7850 kg/m³. The specific strength (tensile strength divided by density) of typical structural aluminium alloys is higher than that of mild steel, making aluminium much more attractive for weight-sensitive applications. Aluminium also naturally forms a protective oxide layer, so it resists atmospheric corrosion without painting. Mild steel is cheaper and easier to weld on site, but for a portable bridge the mass saving is critical: an aluminium structure can be lifted and transported by a smaller crew. Therefore, aluminium alloy is the recommended choice despite higher material cost.
铝合金的密度约为 2700 kg/m³，而低碳钢约为 7850 kg/m³。典型结构铝合金的比强度（抗拉强度除以密度）高于低碳钢，因此在注重自重的应用中优势明显。铝材还能自然形成保护性氧化膜，无须涂装即可抵抗大气腐蚀。低碳钢成本低且现场焊接方便，但对于一座便携桥，减重至关重要：铝结构可由更少的人力搬运和运输。因此，尽管材料成本较高，仍推荐铝合金。
2. Understanding Ferrous and Non-Ferrous Metals | 理解黑色金属与有色金属
The question asked: "Classify the following metals as ferrous or non-ferrous: cast iron, copper, stainless steel, zinc. Describe the key difference between the two groups and give a practical example where each type is preferred."
题目问到："将下列金属分类为黑色或有色金属：铸铁、铜、不锈钢、锌。描述两类金属的主要区别，并各举一个适用实例。"
Ferrous metals contain iron as the main element; examples include cast iron and stainless steel (an alloy of iron, chromium, and nickel). Non-ferrous metals contain no iron; examples are copper and zinc. The fundamental difference is that ferrous metals are generally magnetic and, except for stainless steel, tend to rust when exposed to moisture. Non-ferrous metals are non-magnetic and often have excellent corrosion resistance and electrical conductivity. A cast iron machine base benefits from vibration damping, while copper is chosen for electrical wiring because of its low resistivity.
黑色金属以铁为主要元素，如铸铁和不锈钢（铁、铬、镍的合金）。有色金属不含铁，如铜和锌。根本区别在于黑色金属一般具有磁性，且除不锈钢外，遇湿容易生锈。有色金属无磁性，通常具有出色的耐腐蚀性和导电性。铸铁机床底座可利用其吸振性，而铜因低电阻率被选作电线材料。
3. Casting vs. Forging Processes | 铸造与锻造工艺
The question asked: "A company is deciding whether to use sand casting or drop forging to produce a medium-volume batch of steel gear blanks. State one advantage and one disadvantage of sand casting compared with drop forging."
题目问到："某公司需生产中批量的钢齿轮毛坯，正在考虑砂型铸造或落锤锻造。对比落锤锻造，说出砂型铸造的一个优点和一个缺点。"
Sand casting can accommodate complex geometries, including internal cavities, without needing expensive tooling; it is economical for small to medium production runs. However, cast parts generally exhibit a rougher surface finish and lower dimensional accuracy, which may require additional machining. Drop forging, by contrast, aligns the grain structure of the metal, giving the gear higher strength and fatigue resistance, but it demands costly dies and is less suitable for intricate shapes. Thus sand casting offers design flexibility, though at the expense of mechanical properties and precision.
砂型铸造可成形复杂几何形状（包括内腔），且无需昂贵模具，适合中小批量生产。然而，铸件表面通常较粗糙、尺寸精度较低，可能需额外机加工。相反，落锤锻造能使金属晶粒流线定向排列，赋予齿轮更高的强度和疲劳抗力，但需要昂贵的模具且不适合复杂形状。因此砂型铸造提供了设计灵活性，但牺牲了力学性能和精度。
4. Soldering and PCB Assembly | 焊接与PCB组装
The question asked: "When soldering a through-hole resistor onto a printed circuit board, what soldering iron temperature range should be used for lead-free solder? Explain why flux is essential in the soldering process."
题目问到："使用无铅焊锡将通孔电阻焊到印制电路板上时，烙铁应设置的温度范围是多少？解释为何助焊剂在焊接过程中必不可少。"
For lead-free solder (typically a tin-copper or tin-silver-copper alloy), the soldering iron tip temperature is normally set between 300 °C and 350 °C. Flux plays two key roles: it removes existing oxide layers from the component lead and the copper pad, and it shields the clean metal surfaces from re-oxidation during heating. This allows the molten solder to wet the joint effectively, forming a shiny, reliable electrical and mechanical connection. Without flux, a cold or dry joint is likely, leading to intermittent faults.
对于无铅焊锡（通常为锡铜或锡银铜合金），烙铁头温度一般设定在 300 °C 至 350 °C。助焊剂起两个关键作用：去除元件引脚和铜焊盘上的氧化层，并在加热时保护洁净金属表面不被再次氧化。这样熔融焊锡才能有效润湿焊点，形成光亮、可靠的电学和机械连接。若无助焊剂，极易出现虚焊，导致间歇性故障。
5. Calculating Series Resistance | 串联电阻计算
The question asked: "Two resistors, 220 Ω and 330 Ω, are connected in series across a 9 V battery. Calculate the total resistance and the current flowing in the circuit. Show your working."
题目问到："两个电阻 220 Ω 和 330 Ω 串联后接在 9 V 电池两端。计算总电阻和电路中的电流，写出步骤。"
For resistors in series, the total resistance is the sum: Rtotal = 220 Ω + 330 Ω = 550 Ω. Using Ohm's Law, the current I is given by I = V ÷ Rtotal essed as 16.4 mA. The series circuit has the same current flowing through both resistors, and the voltage divides according to each resistance value.
Rtotal = R1 + R2, I = V / Rtotal
串联电阻的总电阻为各电阻之和：R总 = 220 Ω + 330 Ω = 550 Ω。根据欧姆定律，电流 I = V ÷ R总 = 9 V ÷ 550 Ω ≈ 0.01636 A，即 16.4 mA。串联电路中流过两个电阻的电流相同，电压按阻值比例分配。
6. Gear Trains and Velocity Ratio | 齿轮系与速度比
The question asked: "A driver gear has 20 teeth and meshes with a driven gear of 60 teeth. If the driver rotates at 120 rpm, determine the velocity ratio and the output speed of the driven gear. State whether this system increases speed or torque."
题目问到："驱动齿轮有 20 齿，与一 60 齿的从动齿轮啮合。驱动轮转速为 120 rpm，求速度比和从动轮的输出转速，并
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