📚 A-Level Science: Common Mistake Questions Explained | A-Level 科学：易错题精讲
A-Level Science examinations often contain questions that trip up even well-prepared students. These tricky questions frequently test subtle concepts, common misconceptions, or the ability to apply knowledge to unfamiliar contexts. This article highlights some of the most frequent mistakes in Physics, Chemistry, and Biology, and provides clear explanations to help you avoid them.
A-Level科学考试中常有一些题目会让准备充分的学生也犯错。这些易错题往往考查细微的概念、常见的误解，或者将知识应用到不熟悉场景的能力。本文精选了物理、化学、生物中最常见的错误，并提供清晰的解析，帮助你避开这些陷阱。
1. Misreading Velocity-Time Graphs | 误读速度-时间图像
A common exam question gives a velocity-time (v-t) graph and asks for displacement or acceleration. Students often confuse the meaning of the slope and the area. The slope of a v-t graph gives acceleration, while the area under the graph gives displacement. A typical mistake is to calculate displacement by multiplying final velocity by time, or to use the slope to find displacement.
常见的考题会给出速度-时间（v-t）图，并要求求位移或加速度。学生常混淆斜率和面积的含义。v-t 图的斜率表示加速度，而图下方的面积表示位移。一个典型错误是用末速度乘时间来算位移，或者用斜率求位移。
Example: ½ × 10 s × 20 m/s = 100 m. Many incorrectly use distance = speed × time = 20 × 10 = 200 m.
示例：一辆汽车从静止匀加速到20 m/s用时10 s，在v-t图上是直线。正确的位移是三角形面积：½ × 10 s × 20 m/s = 100 m。许多人错误使用路程=速度×时间=20×10=200 m。
2. Confusing Newton's Third Law Pairs | 混淆牛顿第三定律中的作用力与反作用力
Newton's third law states that if body A exerts a force on body B, then body B exerts an equal and opposite force on body A. These forces act on different bodies and are of the same type. A classic error is to identify the weight of a book and the normal force from the table as an action-reaction pair. In reality, the weight is the gravitational pull of the Earth on the book; its reaction is the gravitational pull of the book on the Earth. The normal force on the book from the table is paired with the normal force on the table from the book.
牛顿第三定律指出，若物体A对物体B施加一个力，则物体B同时向物体A施加一个大小相等、方向相反的力。这两个力作用在不同物体上且属于同种类型。一个经典错误是将书的重力与桌面的支持力视为一对作用力与反作用力。实际上，书的重力是地球对书的引力，其反作用力是书对地球的引力。桌面对书的支持力与书对桌面的压力是一对作用力与反作用力。
Exam questions may ask to identify the reaction to a given force. Always check: do the forces act on two different objects? Are they the same type (e.g. both gravitational, both contact)? If they act on the same object or are different types, they are not a third-law pair.
考题可能会要求找出某个力的反作用力。请始终检查：这两个力是否作用在两个不同的物体上？它们是否属于同一类型（例如都是引力，都是接触力）？如果它们作用在同一物体
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