Year 7 Cambridge Physics: Practical Assessment Key Points

📚 Year 7 Cambridge Physics: Practical Assessment Key Points | 实验考核要点

Practical work is a core part of Year 7 Cambridge Physics. Whether you are preparing for a Checkpoint progression test, an end-of-unit investigation, or just building your lab skills, understanding how to approach experiments safely and accurately will boost both your confidence and your marks. This guide breaks down the key skills examiners look for in practical assessments and gives you clear, step-by-step tips on how to demonstrate them.

实验操作是七年级剑桥物理的核心部分。无论你是在为Checkpoint阶段测试、单元结束探究任务做准备，还是在培养实验室技能，懂得如何安全、准确地进行实验不仅能增强信心，也能显著提高评分。本指南详细拆解了实验考核中评分者关注的关键技能，并为你提供清晰、实用的操作要点。

1. Safety in the Physics Lab | 物理实验室安全

Always wear safety goggles when using Bunsen burners, heating water, stretching springs or dealing with any projectiles. Goggles protect your eyes from burns, splashes and flying objects.

使用本生灯、加热水、拉伸弹簧或涉及任何抛射物体时，务必佩戴护目镜。护目镜可以保护眼睛免受灼伤、液体飞溅和飞溅物体的伤害。

Report any breakage such as a snapped rubber band or a cracked beaker immediately to your teacher. Never pick up broken glass with bare hands; use a dustpan and brush.

如有任何破损（例如橡皮筋断裂或烧杯裂开）应立即报告老师。切勿徒手捡拾碎玻璃，应使用簸箕和刷子。

Keep your work area tidy. Bags, coats and stools should be well away from the walkway to prevent tripping hazards during an experiment.

保持实验区域整洁。书包、外套和凳子应远离过道，以免在实验过程中造成绊倒隐患。

2. Using Measuring Instruments | 使用测量仪器

In Year 7 physics, you will use a ruler, stopwatch, thermometer, mass balance, forcemeter (newton meter) and ammeter. Always choose the instrument with the appropriate range and precision for the quantity you are measuring.

七年级物理中你会用到直尺、秒表、温度计、质量天平、测力计（牛顿计）和电流表。务必选择量程和精度适合被测量的仪器。

Before starting, check that the instrument reads zero. For a mass balance, press the tare button; for a forcemeter, make sure the pointer is exactly at zero when unloaded. This prevents zero error.

开始测量前，检查仪器是否归零。质量天平应按去皮键；测力计在空载时要确保指针恰好指零。这样做可以避免零误差。

When measuring length with a ruler, avoid parallax error by placing your eye directly in line with the mark. The same rule applies when reading a thermometer or a measuring cylinder.

用直尺测量长度时，眼睛要与刻度线平视，以避免视差错误。读取温度计或量筒的液面时同样遵循平视原则。

3. Reading Scales and Uncertainty | 读取刻度与不确定度

Every measurement has an uncertainty. For a ruler marked in millimetres, the smallest division is 1 mm, so the uncertainty is ±0.5 mm. Always record measurements to the nearest half-division: e.g., 12.3 cm (123 mm) rather than just 12 cm.

任何测量都存在不确定度。以毫米为刻度的直尺，最小分度是1 mm，不确定度就是±0.5 mm。记录测量值时应读取到最近半分度，例如写为12.3 cm（123 mm），而不是约12 cm。

With a stopwatch, human reaction time introduces about ±0.2 s uncertainty. When timing a pendulum, measure the time for 10 swings (N = 10) and then divide to find the period. This reduces the impact of reaction error.

使用秒表时，人的反应时间会带来约±0.2 s的不确定度。在测量单摆周期时，可记录10次摆动（N=10）的总时间，再除以次数，以减小反应误差的影响。

Digital instruments display digits; the uncertainty is usually ±1 in the last digit. For example, if a digital balance shows 45.2 g, the true value lies between 45.1 g and 45.3 g.

数字仪器的显示具有末位不确定性，通常为最后一位数字的±1。比如数字天平显示45.2 g，真实值在45.1 g和45.3 g之间。

4. Recording Data in Tables | 表格记录数据

All data must be presented in a ruled table with clear headings. The first column is usually the independent variable (the one you change), and the second is the dependent variable (the one you measure).

所有数据都必须呈现在带有线框的表格中，并写明表头。第一列通常是自变量（你改变的变量），第二列是因变量（你测量的变量）。

Every heading must include the quantity and its unit, separated by a slash, e.g., ‘Length l / cm’ or ‘Time t / s’. Never write the unit inside the data cells.

每个表头必须注明物理量和单位，中间用斜线分隔，如“长度 l / cm”或“时间 t / s”。切勿把单位写在数据单元格内。

Record values consistently to the same number of decimal places. If you measure length to 0.1 cm, every entry in that column should end with a tenth digit, even if it is a zero.

记录数值时保持统一的小数位数。若长度测量精确到0.1 cm，该列中每项都应保留一位小数，即使末位是零也要写出。

Length l / cm	Time t / s
20.0	1.8
40.0	2.6
60.0	3.2

5. Drawing Graphs | 绘制图表

Plot the independent variable on the horizontal x-axis and the dependent variable on the vertical y-axis. Label each axis with the quantity and unit, e.g., ‘Mass m / g’.

将自变量画在水平 x 轴上，因变量画在垂直 y 轴上。每个坐标轴都标出物理量和单位，如“质量 m / g”。

Choose a scale that uses more than half of the graph paper and goes up in simple steps like 1, 2, 5, 10. Do not use awkward scales such as 3 or 7 per division.

选择能利用大半坐标纸的标度，并以1、2、5、10等简单步长递增。不要采用每个分格代表3或7这样难以读取的标度。

Plot points as small, sharp crosses (×) or dots in circles. Draw a single smooth best-fit straight line or curve through the points, ignoring any outliers. Never do dot-to-dot.

描点使用清晰的小叉号（×）或带圆圈的点。穿过数据点画出一条平滑的最佳拟合直线或曲线，忽略明显偏离的点。绝不要逐点连线。

If the line is straight and passes through the origin, you can state that the two variables are directly proportional:

若直线通过原点，可说明两个变量成正比关系：

y ∝ x or y = k x

6. Identifying Variables | 识别变量

In any fair test you must identify three types of variable: independent (the one you change), dependent (the one you measure), and control variables (those kept constant to ensure a fair test).

在任何公平实验里，你都必须识别三类变量：自变量（你改变的）、因变量（你测量的）和控制变量（为公平测试而保持不变的因素）。

For a spring extension experiment, the independent variable is the force applied (mass hanged), the dependent is the extension of the spring, and control variables include the same spring, room temperature and starting length.

在弹簧伸长实验中，自变量是施加的力（悬挂的质量），因变量是弹簧的伸长量，控制变量包括使用同一根弹簧、室温和起始长度。

Explicitly state at least two control variables in your plan. Use phrases like ‘keep the mass of the trolley constant’ or ‘use the same thickness of wire’.

在实验计划中明确写出至少两项控制变量。使用类似“保持小车质量不变”或“使用相同粗细的导线”这样的表述。

7. Writing a Method | 撰写实验方法

Write the method as a logically ordered list of steps using command verbs. Begin each step with ‘Measure’, ‘Record’, ‘Adjust’, ‘Repeat’, etc.

将实验方法写成逻辑清晰的步骤列表，并使用指令动词。每一步以“测量”“记录”“调节”“重复”等词开头。

A typical structure: Set up the apparatus as shown. Measure and record the initial length. Add a mass of 50 g. Measure the new length. Calculate the extension. Repeat for a range of masses.

典型结构为：按照图示搭建装置。测量并记录初始长度。添加一个50 g的砝码。测量新长度。计算伸长量。对不同质量重复上述步骤。

Always include a step about repeating measurements and calculating an average to improve reliability. Remove anomalous values before averaging.

务必加入重复测量并计算平均值以提高可信度的步骤。计算平均值前先剔除异常值。

8. Calculating Averages and Handling Errors | 计算平均值与误差处理

When you have repeated readings, find the arithmetic mean: add the values and divide by the number of readings. For three times (t₁, t₂, t₃), the average time tₐᵥ is

多次读数时，计算算术平均值：将数值相加后除以读数次数。对于三次时间记录(t₁, t₂, t₃)，平均时间 tₐᵥ 为

tₐᵥ = (t₁ + t₂ + t₃) / 3

Identify an anomalous result as one that is very different from the pattern. In a table of elongations increasing smoothly, a sudden drop or a value twice as large suggests a mistake in reading or recording.

异常结果是指明显偏离整体规律的数据点。在一系列均匀增加的伸长量中，突然下降或数值翻倍，多半是读数或记录错误。

Never alter original data; simply put a circle around the anomalous point and exclude it from the average calculation. Mention it in your evaluation.

永远不要修改原始数据；只用圆圈将异常点标出，并在计算平均值时予以剔除，同时在实验评估部分说明。

9. Drawing Conclusions | 得出结论

A conclusion must refer directly to the data or graph. Use sentence starters like ‘As the mass increased, the extension also increased’ or ‘The graph shows a straight line through the origin, which means extension is directly proportional to the force.’

结论必须直接引用数据或图表。可使用“随着质量增大，伸长量也增大”或“图像为通过原点的直线，说明伸长量与力成正比”这样的句式。

Avoid vague statements like ‘it worked well’. Compare your findings with the scientific prediction. For a pendulum, you might state: ‘The period increased with length, which agrees with the idea that longer pendulums swing more slowly.’

避免使用“实验效果不错”等模糊表述。将结果与科学预测进行对比。例如研究摆时可以说：“周期随摆长增加而增大，这与长摆摆动更慢的道理相符。”

Use numbers from the table or graph to support your conclusion. For instance: ‘When the force doubled from 2 N to 4 N, the extension also roughly doubled from 3.1 cm to 6.0 cm.’

用表格或图表中的具体数字支撑结论。例如：“当力从2 N加倍到4 N时，伸长量也大致从3.1 cm加倍到6.0 cm。”

10. Evaluating the Experiment | 评估实验

An evaluation discusses how reliable and accurate the results are, and suggests improvements. Comment on anomalous results, sources of error, and whether the data supports the conclusion strongly.

评估部分讨论结果的可靠性与准确度，并提出改进建议。要评论异常结果、误差来源以及数据是否能充分支持结论。

Common sources of error in Year 7 experiments: parallax when reading a ruler, reaction time when using a stopwatch, friction in a pulley, and zero error in meters. For each error, suggest a practical improvement.

七年级实验中常见的误差来源有：读数时视差、秒表反应时间、滑轮摩擦以及仪表零点误差。为每项误差提出一项切实可行的改进措施。

For example: ‘To reduce reaction time error, we could use a light gate connected to a timer instead of a manual stopwatch.’ Even if you cannot use it, suggesting it shows evaluative thinking.

例如：“为了减小反应时间误差，我们可以用光门连接计时器代替手动秒表。”即使无法实际使用，提出这一设想也能体现评估思维。

11. Practical Example: Pendulum Period Investigation | 实践案例：摆的周期探究

A classic Year 7 investigation asks: ‘How does the length of a pendulum affect its period?’ You set up a clamp stand, string and a small mass bob. Change the length from 20 cm to 100 cm, keep the angle of swing small (less than 10°) and constant.

经典的七年级探究题是：“摆长如何影响单摆的周期？”你需搭建铁架台、细线和一个小摆锤。将摆长从20 cm改变到100 cm，保持摆动角度小（少于10°）且恒定。

Time 10 complete swings, record in a table, and calculate the period T = t / 10. Plot a graph of T² against length l if you want a straight line, or T against l for a curved relationship.

记录10次完整摆动的时间，列表并计算周期 T = t / 10。若希望得到直线，可作 T²–l 图；作 T–l 图则会得到曲线关系。

T = t / 10 (T² ∝ l)

In your conclusion, state that a longer pendulum gives a longer period. Evaluate by noting that starting the stopwatch exactly at the mid-point of the swing was difficult – a magnet-and-sensor timer would improve accuracy.

结论中写明摆长越长周期越大。评估时可指出，在摆动中点精准启动秒表较困难，使用磁敏传感器计时可以提高准确度。

12. Revision Tips for Practical Exams | 实践考试复习技巧

Re-draw graphs from your lab book without looking at the original; practise choosing scales and labelling axes. Learn the standard formats for result tables and graph-plotting rules.

不看原图，按照实验记录本重新绘制图表；练习选取标度和标注坐标轴。熟记标准的结果表格格式和作图规则。

Write out a method for a common experiment, such as ‘finding the density of an irregular solid’, and then check you have included control variables, repeats and safety notes.

为常见的实验写出完整步骤，如“测量不规则固体的密度”，然后检查是否包含了控制变量、重复实验和安全注意事项。

Use the keywords examiners love: ‘independent variable’, ‘dependent variable’, ‘fair test’, ‘precise to ±0.5 mm’, ‘anomalous’, ‘reliable’, ‘best-fit line’, ‘directly proportional’, and ‘improvement’. Spelling them correctly shows understanding.

用好评分者欣赏的关键词：“自变量”“因变量”“公平实验”“精度为±0.5 mm”“异常”“可靠”“最佳拟合线”“成正比”和“改进措施”。正确拼写能有效展示你真的理解了。

Finally, during the practical test, read the question twice, set up apparatus calmly, and record readings immediately. You’ve got this!

最后，实践测试时先把题目读两遍，沉着搭建装置，并即时记录读数。你一定可以做到！

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Year 7 Cambridge Physics: Practical Assessment Key Points | 实验考核要点