📚 Year 9 CAIE Physics: Key Points for Experimental / Practical Assessments | Year 9 CAIE 物理：实验/实践考核要点
Year 9 CAIE Physics practical assessments test your ability to plan experiments, use measuring instruments, collect and process data, and evaluate results. You are expected to demonstrate safe practice, accurate observation, and logical reasoning. This guide focuses on the most common practical skills and investigations that appear in the Year 9 syllabus, giving you the key points you need to revise.
Year 9 CAIE 物理实践考核考查你设计实验、使用测量仪器、收集处理数据以及评估结果的能力。你需要展现安全操作、精确观察和逻辑推理。本指南聚焦 Year 9 大纲中最常见的实验技能和研究课题，帮助你提炼出必须掌握的复习要点。
1. Accurate Measurement of Length and Volume | 长度与体积的精确测量
Length measurements require you to choose the right instrument, such as a metre rule or a vernier caliper. Place the zero mark exactly at one end of the object and read the scale with your eye directly in line with the marking to avoid parallax error. Always record the raw measurement with its unit, repeating the measurement and finding the average to improve reliability.
测量长度需要选择合适的仪器，如米尺或游标卡尺。将零刻度对准物体一端，视线与刻度垂直读数，以避免视差误差。必须记录带有单位的原始测量值，并重复测量取平均值，以提高可靠性。
. Irregular objects require the displacement method: partly fill a measuring cylinder with water, note the initial volume, then carefully lower the object into the water and record the new reading. The difference gives the volume of the object. Always read the bottom of the meniscus at eye level.
对于体积，规则固体可以用长×宽×高计算。不规则物体需要使用排水法：先在量筒中加入部分水，记下初始体积，然后将物体小心沉入水中，记下新的读数。两次读数之差即为物体的体积。必须在视线水平处读取凹液面的最低点。
2. Determining Density of Solids and Liquids | 固体和液体密度的测定
Density is defined as mass per unit volume, and the formula is displayed below. You will measure mass using a digital balance and determine volume either by geometry or by the displacement method.
密度定义为单位体积的质量，计算公式如下所示。你将使用电子天平测量质量，并通过几何方法或排水法测定体积。
ρ = m / V
³. For a liquid, measure the mass of an empty measuring cylinder, pour the liquid in, measure the new mass, and subtract to obtain the liquid's mass. The volume is read directly from the cylinder.
对于如金属立方体的规则固体，用天平测其质量 m，测量边长并计算 V = 边长³。对于液体，先测量空量筒的质量，倒入液体后再测量总质量，相减得到液体的质量。体积直接由量筒读取。
A typical data table for a solid using displacement is shown below. Notice the units are included in the headings, and all readings are recorded to the same precision.
下面展示了使用排水法测定固体密度的典型数据表。请注意表格标题中已包含单位，且所有读数都保留相同精度。
| Object | Mass m (g) | Initial volume V₁ (cm³) | Final volume V₂ (cm³) | Volume V = V₂ − V₁ (cm³) | Density ρ (g/cm³) |
|---|---|---|---|---|---|
| Steel ball | 50.0 | 50.0 | 56.2 | 6.2 | 8.06 |
Always repeat the experiment, calculate the mean density and compare it with accepted values. Anomalous results, such as a density far from the average, should be identified and excluded from the mean.
务必重复实验，计算密度平均值并与公认值比较。异常结果，例如远离平均值的密度，应识别出来并从平均值计算中剔除。
3. Investigating Springs: Hooke's Law | 弹簧研究：胡克定律
Hooke’s Law states that the extension of a spring is directly proportional to the applied force, provided the elastic limit is not exceeded. The relationship is written as:
胡克定律指出，在弹性限度内，弹簧的伸长量与施加的力成正比。关系式写作：
F = k × e
re its original length. Add slotted masses one by one, recording the new length each time. The extension e = stretched length − original length. Use F = m × g to convert mass to force (take g = 10 N/kg).
其中 F 是力（单位牛顿），e 是伸长量（单位米），k 是劲度系数。研究此规律时，垂直悬挂弹簧并测量其原长。依次添加槽码，并记录每次的新长度。伸长量 e = 伸长后长度 − 原长。使用 F = m × g 将质量转换为力（取 g = 10 N/kg）。
Plot a graph of force (y-axis) against extension (x-axis). A straight line through the origin confirms Hooke’s Law, and the gradient equals the spring constant k. If the graph begins to curve, you have exceeded the elastic limit and the spring may be permanently deformed.
绘制力（y 轴）与伸长量（x 轴）的关系图。一条通过原点的直线验证胡克定律，斜率等于劲度系数 k。如果图形开始弯曲，说明已经超过弹性限度，弹簧可能会永久变形。
Control variables in this experiment include using the same spring throughout and ensuring that masses are added gently, without bouncing. Also, align your eye perpendicularly when measuring length to reduce parallax.
本实验的控制变量包括始终使用同一根弹簧，并确保轻轻添加槽码、避免晃动。同时，测量长度时视线要垂直以减少视差。
4. Measuring Average Speed | 测量平均速度
The average speed of an object can be calculated using the equation:
物体的平均速度可用以下公式计算：
v = s / t
where s is the distance travelled and t is the time taken. In a typical practical, you will let a trolley roll down a ramp and measure the time it takes to cover a marked distance using a stopwatch. Repeat the run at least three times and calculate the mean time to improve accuracy.
其中 s 是移动距离，t 是所用时间。在典型实验中，你让小车从斜面滑下，用秒表测量它通过指定距离的时间。至少重复三次并计算平均时间，以提高准确度。
It is essential to use the same starting point for each trial and to release the trolley without pushing it. You may vary the angle of the slope and observe how speed changes. Also, you can use a ticker tape timer to obtain more precise time intervals and plot a distance–time graph from the dots.
每一次试验必须使用相同的起点，并且释放小车时不要用力推。你可以改变斜面角度并观察速度如何变化。此外，还可使用打点计时器获得更精确的时间间隔，并根据打点绘制距离–时间图。
When analysing the results, keep the ruler aligned and the stopwatch button pressed at the exact instant the trolley passes the mark. Reaction time error can be reduced by using light gates, but if using a stopwatch, practise a consistent counting rhythm.
分析结果时，要使直尺对准，并在小车恰好通过标记的瞬间按下秒表。可通过使用光闸减少反应时间误差，但若使用秒表，则要练习一致的计数节奏。
5. Setting Up Circuits and Using Ammeters and Voltmeters | 搭建电路与使用电流表电压表
Correct circuit construction is essential for all electrical investigations. An ammeter is always connected in series so that the current flows through it, while a voltmeter is connected in parallel across the component you wish to measure. Always start with the switch open and check connections before closing the circuit.
正确的电路搭建是所有电学实验的基础。电流表必须串联，使电流流过它；电压表则并联在待测元件两端。开始时务必保持开关断开，并在闭合电路前检查所有连接。
Both meters have positive and negative terminals; the positive terminal must be connected to the side that is closer to the positive end of the power supply. If connected backwards, the pointer may deflect below zero and damage the meter. Choose a suitable range — if you are unsure, start with the highest range and move down.
两种表都有正负接线柱；正接线柱必须连接到更靠近电源正极的一侧。如果接反，指针可能反向偏转并损坏电表。选择合适的量程——如果不确定，先从最大量程开始，再逐步降低。
Record each reading with its unit, and always tap the meter gently to ensure the pointer is not sticking. Before any measurement, check the zero error: when no current flows, the needle should point exactly at zero; if not, adjust it using the zero-adjust screw.
记录每一个读数及其单位，并轻敲电表以确保指针没有卡住。测量前检查零误差：无电流时指针应指向零位；若不是，则用调零螺丝调零。
6. Ohm's Law and Resistance of a Wire | 欧姆定律与导线电阻
Ohm’s Law states that the current through a conductor is proportional to the potential difference across it, provided temperature remains constant. The resistance R is given by:
欧姆定律指出，在温度不变的条件下，通过导体的电流与导体两端的电势差成正比。电阻 R 由下式给出：
R = V / I
A common investigation explores how the length of a wire affects its resistance. Set up a circuit with a battery, a switch, an ammeter in series, and a voltmeter connected across the test wire. Use crocodile clips to change the effective length L of the wire. For each length, close the switch briefly, record V and I, and calculate R.
一个常见的探究实验是研究导线长度如何影响其电阻。将电池、开关、串联的电流表和并联在待测导线两端的电压表接入电路。使用鳄鱼夹改变导线的有效长度 L。对于每个长度，短暂闭合开关，记录 V 和 I，并计算 R。
You should find that resistance increases with length, which is consistent with R ∝ L for a uniform wire. Plot R against L; a straight line through the origin supports the relationship. Control variables: keep the wire material and thickness the same, and avoid high currents that could raise the wire's temperature.
你会发现电阻随长度增加，这与均匀导线 R ∝ L 一致。绘制 R–L 图，若为通过原点的直线，则支持该关系。控制变量：保持导线材料和粗细相同，并避免大电流使导线温度升高。
Voltmeter and ammeter readings should be taken quickly to minimise heating. Anomalous points, often caused by poor clip contact, should be identified. Repeating and averaging further reduce random errors.
电压表和电流表的读数应快速记录，以减小发热影响。通常由于鳄鱼夹接触不良产生的异常点应被识别出来。重复实验并取平均值可进一步减小随机误差。
7. Law of Reflection Using a Ray Box | 利用光线盒研究反射定律
The law of reflection states that the angle of incidence i equals the angle of reflection r, both measured from the normal. To verify this, place a plane mirror on a sheet of white paper, draw its outline and a normal line perpendicular to the mirror surface. Direct a single ray from a ray box toward the mirror along a chosen incident ray.
反射定律指出入射角 i 等于反射角 r，两者均从法线量起。为了验证这一规律，将平面镜放在一张白纸上，画出镜子轮廓和垂直于镜面的法线。用光线盒射出一条细光束，沿选定的入射光线射向镜面。
cident angles (e.g. 20°, 30°, 40°, 50°). Record your measurements in a table and check that i ≈ r within experimental uncertainty.
用铅笔点标记入射光线和反射光线，移走镜子后用直角器测量 i 和 r。对不同入射角（例如 20°、30°、40°、50°）重复此过程。将测量值记录在表格中，并检查在实验不确定度范围内是否满足 i ≈ r。
Precautions include: ensuring the mirror is upright and not titled sideways, using a sharp pencil for thin ray marks, and aligning the protractor carefully with the normal. Also, work in a slightly darkened room to make the rays clearly visible.
注意事项包括：确保镜子竖直、不歪斜，使用削尖的铅笔画出纤细的光线标记，并使量角器与法线仔细对齐。此外，在稍暗的房间操作使光线清晰可见。
8. Handling Data: Tables and Calculations | 数据处理：表格与计算
Good data presentation starts with a well-drawn table. The independent variable (the one you change) should appear in the first column, and the dependent variable (the one you measure) in the subsequent columns. Every column heading must include the name of the quantity and its unit, separated by a slash, e.g. 'Length L / cm'.
好的数据呈现始于一张绘制清晰的表格。自变量（你改变的变量）应放在第一列，因变量（你测量的变量）放在其后的列。每一列的标题必须包含物理量名称及单位，以斜线分隔，如“长度 L / cm”。
All readings should be recorded to the same number of decimal places, consistent with the precision of the instrument. For example, if a metre rule allows readings to 0.1 cm, every length in that table must end in .0 or .5 etc. Calculated quantities such as density or resistance should be given to an appropriate number of significant figures.
所有读数应记录到相同的小数位数，与仪器的精度匹配。例如，若米尺能读到 0.1 cm，则表中每个长度数值都必须以 .0 或 .5 等结尾。计算得到的量（如密度或电阻）应保留恰当的有效数字。
Whenever possible, calculate the mean of repeated measurements and compare individual readings to identify outliers. If a value is clearly inconsistent, mark it as anomalous, exclude it from the mean, and suggest a reason in your evaluation. This shows critical thinking.
只要可能，应计算重复测量的平均值，并对比各次读数来识别异常值。如果某个数值明显不一致，将其标记为异常，排除在平均值之外，并在评估中说明原因。这体现出批判性思维。
9. Graph Skills and Analysis | 图表技巧与分析
you to extract further information. Always label the axes with the quantity and unit, e.g. 'Force F / N' and 'Extension e / cm' ections. Use a simple scale (e.g. one large square = 2, 5, or 10 units) for easy plotting.
图表能让规律可视化并帮助你提取更多信息。坐标轴必须标注物理量和单位，例如“力 F / N”和“伸长量 e / cm”。比例尺应使描点占据图纸两个方向的一半以上空间。使用简单的比例（如一大格代表 2、5 或 10 个单位）便于描点。
or dots with circles around them. Draw either a best-fit straight line or a smooth curve that follows the trend of the points. Do not join dot-to-dot unless the question specifically asks for it. Identify and label any anomalous point that falls far from the line.
用小的叉号 (×) 或加圈点描出数据点。画一条最佳拟合直线或平滑曲线，以显示点的整体趋势。除非题目明确要求，否则不要逐点连线。识别并标注远离直线的任何异常点。
If the graph yields a straight line through the origin, the variables are directly proportional. The gradient can be calculated by picking two points on the line (not necessarily data points) and using Δy/Δx. The physical meaning of the gradient gives, for instance, the spring constant or resistance per unit length.
若图形是一条通过原点的直线，则变量成正比关系。可在直线上取两点（不一定是原始数据点）计算斜率 Δy/Δx。斜率的物理意义，例如，代表劲度系数或单位长度电阻。
10. Errors, Uncertainties and Improvements | 误差、不确定度与改进方法
No measurement is perfect. Random
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