📚 AQA AS Physics Unit 5 (Electricity) – June 2019 Mark Scheme Deep Dive | AQA AS 物理 单元5（电学）2019年6月评分标准深度解析
The June 2019 AQA AS Physics examination included a range of questions that tested the Electricity content – known as Unit 5 in the AS specification. The mark scheme for this paper is an essential tool for understanding exactly what examiners reward: precise definitions, correct equations with units, careful graph analysis, and logical explanations. In this article, we explore the key patterns and marking points from that June 2019 mark scheme, offering a bilingual guide to help you maximise your own marks in the AS Physics examination.
2019年6月的AQA AS物理考试包含了考察电学（AS大纲中的单元5）的大量题目。该试卷的评分标准是理解考官究竟如何给分的关键工具：精确的定义、带单位的正确方程、严谨的图表分析，以及逻辑清晰的解释。本文章将剖析2019年6月评分标准的典型模式和给分点，提供中英双语的指南，帮助你在AS物理考试中获得最高分。
1. Definitions and Units – The Foundation of Mark Points | 1. 定义与单位 – 给分点的基础
The mark scheme for June 2019 consistently rewarded candidates who could state standard definitions using the exact terms from the AQA specification. For example, current is defined as “the rate of flow of charge through a cross-sectional area”, and potential difference is “the energy transferred per unit charge”. These definitions must include the correct quantity and direction – examiners do not accept vague descriptions like “the amount of electricity” or “voltage”. The mark scheme often allocates one mark for the correct equation or worded definition, and a second mark for the units.
2019年6月的评分标准一贯奖励那些能用AQA大纲中的准确术语表述标准定义的考生。例如，电流的定义是“电荷通过横截面的速率”，电势差是“每单位电荷转移的能量”。这些定义必须包含正确的量和方向——考官不接受诸如“电的数量”或“电压”这类模糊的描述。评分标准通常为正确的方程或文字定义分配1分，并为单位再分配1分。
When writing definitions, always include the magnitude and the direction for vector-like quantities, and give the SI units in both symbol and full form. For example, resistivity is defined as “the resistance of a material of unit length and unit cross-sectional area” – not simply “how much it resists”. The mark scheme also checks that you do not confuse resistivity with resistance; this is a frequent source of lost marks. Always write the unit of resistivity as Ω m, and distinguish it clearly from Ω (resistance).
在书写定义时，始终包括大小和方向（对于矢量类量），并同时给出符号和完整形式的SI单位。例如，电阻率被定义为“单位长度和单位横截面积的材料的电阻”——而不是简单称为“它有多阻碍”。评分标准也检查你是否将电阻率与电阻混淆；这是常见的失分点。始终将电阻率的单位写为Ω m，并清楚区分Ω（电阻）与Ω m（电阻率）。
2. Core Calculations – Equations, Working and Units | 2. 核心计算 – 方程、步骤和单位
The June 2019 mark scheme showed that marks are awarded in stages: first for selecting the correct formula, then for correct substitution of values, then for the final answer with the right unit. For example, using the equation R = ρL/A, you must rearrange algebraically before substituting. A common error is to invert the area – the mark scheme penalises this if you do not show the intermediate step. Always write the original equation, then the rearranged form, then the numerical substitution, and finally the answer with a unit.
2019年6月的评分标准显示，分数是按阶段分配的：首先选择正确的公式，然后正确代入数值，最后给出带正确单位的答案。例如，使用方程R = ρL/A时，你必须先进行代数变形再代入。常见错误是将面积颠倒——如果你不写出中间步骤，评分标准会扣分。始终写出原始方程、变形后的形式、数值代入，最后才是带单位的答案。
For calculations involving I = nAve, watch the prefixes. The electron density n is often given in m⁻³, but cross-sectional area may be in mm². Converting to m² requires a factor of 10⁻⁶. The mark scheme for June 2019 explicitly required such conversions to be shown; if you skip the conversion, you lose the substitution mark. Similarly, in P = IV, ensure that the current is in amperes, not milliamperes, unless the final answer is also adjusted.
对于涉及I = nAve的计算，注意前缀。电子密度n通常以m⁻³给出，但横截面积可能以mm²给出。转换为m²需要乘以10⁻⁶。2019年6月的评分标准明确要求展示这种换算；如果跳过换算，你将失去代入分。类似地，在P = IV中，确保电流以安培为单位，而非毫安，除非最终答案同样进行了调整。
Equations that you must know by heart for Unit 5 include: I = ΔQ/Δt, V = W/Q, R = V/I, R = ρL/A, P = VI = I²R = V²/R, and the potential divider equation V_out = V_in × R₂/(R₁ + R₂). In the mark scheme, each equation is a separate mark, so writing it correctly with the right symbols is essential. Do not use capital letters for variables unless they are defined; the mark scheme distinguishes between V (potential difference) and v (drift velocity).
单元5中必须牢记的方程包括：I = ΔQ/Δt, V = W/Q, R = V/I, R = ρL/A, P = VI = I²R = V²/R，以及分压方程V_out = V_in × R₂/(R₁ + R₂)。在评分标准中，每个方程都是单独的一分，因此用正确符号书写至关重要。不要对变量使用大写字母，除非它们有定义；评分标准区分V（电势差）和v（漂移速度）。
3. Circuit Analysis – Series, Parallel and Potential Dividers | 3. 电路分析 – 串联、并联与分压器
The June 2019 mark scheme contained several questions on series and parallel resistor combinations. For series, the total resistance is the sum of individual resistances, and the same current flows through each resistor. For parallel, the reciprocal of total resistance is the sum of reciprocals – a common error is to add resistances directly. The mark scheme often awards one mark for setting up the correct equation, one mark for the calculation, and one mark for the final answer with unit.
2019年6月的评分标准包含了关于串联和并联电阻组合的若干问题。对于串联，总电阻是各个电阻之和，且每个电阻中流过的电流相同。对于并联，总电阻的倒数是各个电阻倒数的和——常见错误是直接相加电阻。评分标准通常为基础方程的正确建立给1分，计算给1分，最终带单位的答案给1分。
Potential divider circuits are a favourite for AQA. The mark scheme expects you to recognise when the circuit is a potential divider and to apply the ratio form. For example, if two resistors R₁ and R₂ are in series across a supply, the voltage across R₂ is V_supply × R₂ / (R₁ + R₂). If a light-dependent resistor (LDR) or thermistor is used as one of the resistors, the mark scheme rewards you for explaining how the resistance changes with light or temperature and how that affects V_out.
分压器电路是AQA的常见考点。评分标准期望你识别电路是否为分压器并应用比例形式。例如，如果两个电阻R₁和R₂串联在电源两端，则R₂两端的电压为V_supply × R₂ / (R₁ + R₂)。如果光敏电阻（LDR）或热敏电阻作为其中一个电阻，评分标准奖励你解释其电阻如何随光或温度变化，以及这如何影响V_out。
When drawing or interpreting circuit diagrams, pay attention to the way the ammeter and voltmeter are connected. An ammeter must be in series, and a voltmeter in parallel. The mark scheme for June 2019 penalised candidates who incorrectly placed a voltmeter in series or an ammeter in parallel. Also, state whether the meters are ideal: ideal ammeters have zero resistance, ideal voltmeters have infinite resistance. This affects calculations involving internal resistance.
在绘制或解释电路图时，注意电流表和电压表的连接方式。电流表必须串联，电压表必须并联。2019年6月的评分标准对错误地将电压表串联或将电流表并联的考生进行了扣分。同时，说明电表是否为理想电表：理想电流表具有零电阻，理想电压表具有无限电阻。这会影响涉及内阻的计算。
4. I–V Characteristics and Component Behaviour | 4. I-V特性与元件行为
The June 2019 mark scheme included questions about current–potential difference (I–V) graphs for different components. For a metallic conductor at constant temperature, the I–V graph is a straight line through the origin, indicating that resistance is constant (Ohm’s law). For a filament lamp, the graph curves upward, showing that resistance increases with current due to increased temperature. For a diode, the graph shows a very small current in the reverse direction and a sharp increase in current after the threshold voltage. The mark scheme rewards labels and shape of the graph, not just a sketch.
2019年6月的评分标准包含了关于不同元件的电流-电势差（I-V）图像的问题。对于恒定温度下的金属导体，I-V图像是一条过原点的直线，表明电阻是恒定的（欧姆定律）。对于白炽灯，图像向上弯曲，表明电阻随电流增大而增大，因为温度升高。对于二极管，图像显示反向电流极小，而在门槛电压之后电流急剧增大。评分标准奖励图像上的标注和形状，而不只是草图。
When drawing I–V graphs, always label the axes with quantity and unit, and mark any intercepts. The gradient of the I–V graph is 1/R for a linear conductor, but for a non-linear component, you must specify the value at a particular point. The mark scheme for June 2019 stated that the reciprocal of the gradient at the origin gives the initial resistance, but that for a lamp the resistance at a specific voltage is found by dividing V by I at that point, not the gradient.
在绘制I-V图像时，始终标注坐标轴的物理量和单位，并标出截距。对于线性导体，I-V图像的斜率为1/R，但对于非线性元件，你必须指定在特定点的值。2019年6月的评分标准指出，原点处斜率的倒数给出初始电阻，但对于灯泡，在特定电压下的电阻是通过该点除以V/I得到的，而不是斜率。
Explain the relationship between temperature and resistance for a metal filament: as the current increases, the filament’s temperature rises, leading to increased lattice vibrations and more collisions for the free electrons. This increases resistance. For a thermistor, increasing temperature decreases resistance because more charge carriers are released. The mark scheme often requires you to mention charge carriers (electrons or ions) and the microscopic mechanism – vague answers like “it gets hotter” do not score full marks.
解释金属灯丝的温度与电阻关系：当电流增大时，灯丝温度升高，导致晶格振动加剧，自由电子的碰撞更频繁。这使电阻增大。对于热敏电阻，升高温度使电阻减小，因为释放出更多的载流子。评分标准常要求你提及载流子（电子或离子）和微观机制——诸如“它变热了”这样模糊的答案无法得到满分。
5. Resistivity and Graph Techniques | 5. 电阻率与图像技巧
One of the main experiments in Unit 5 is measuring the resistivity of a wire. The June 2019 mark scheme focused on the graphical method: measure a length l of the wire, measure its resistance R using an ohmmeter or an ammeter-voltmeter method, and then plot R against l. The gradient of the graph is ρ/A, so if the cross-sectional area A is known, the resistivity ρ can be calculated. The mark scheme expected you to state that the graph must include the origin and be a straight line through the origin if the wire’s temperature is constant.
单元5的主要实验之一是测量金属丝的电阻率。2019年6月的评分标准集中在图像方法上：测量金属丝的长度l，使用欧姆表或电流-电压表方法测量其电阻R，然后绘制R与l的曲线。图像的斜率为ρ/A，因此如果已知横截面积A，就可以算出电阻率ρ。评分标准期望你指出，如果金属丝的温度恒定，图像必须经过原点且为直线。
When plotting a graph for resistivity, use the largest area of the grid available, choose a suitable scale so the gradient is easy to calculate, and include error bars if instructed. The mark scheme awards a mark for calculating the gradient from a chosen triangle with dimensions at least half the length of the line. Always show the calculation of the gradient, not just the value. The unit of the gradient will be Ω m⁻¹, and multiplying by A (m²) gives ρ in Ω m.
在绘制电阻率图像时，使用网格上最大的区域，选择合适的刻度使斜率易于计算，如果指示则需要包括误差棒。评分标准为从所选三角形计算斜率给予一分，三角形的尺寸至少要达到直线长度的一半。始终展示斜率计算过程，而不仅仅给出数值。斜率的单位为Ω m⁻¹，乘以A（m²）得到ρ的单位Ω m。
Graph interpretation in the June 2019 mark scheme also included using the intercept of a V against I graph to find the EMF and internal resistance of a battery. The equation V = E – Ir is plotted as V on the y-axis and I on the x-axis. The intercept on the y-axis gives E, and the negative gradient gives r. The mark scheme demanded that candidates identify which variable is on which axis and state that the gradient is –r, not just “the gradient is r”.
2019年6月评分标准中的图像解读还包括使用V-I图像的交点来求电池的电动势和内阻。方程V = E – Ir绘制为纵轴V、横轴I。纵轴截距给出E，负斜率给出r。评分标准要求考生明确哪个变量在哪个轴上，并说明斜率为–r，而不只是“斜率为r”。
6. Experimental Methods – Circuits and Measurements | 6. 实验方法 – 电路与测量
The mark scheme for June 2019 assessed experimental techniques for measuring resistance, resistivity and internal resistance. For measuring resistivity, you must use a micrometer to measure the diameter of the wire in several places to account for uniform thickness, and calculate the mean area. The mark scheme rewarded the mention of using a micrometer screw gauge because it measures to 0.01 mm. For length, use a metre ruler and measure from the points where the wire makes contact – not the entire wire if crocodile clips are used.
2019年6月的评分标准考察了测量电阻、电阻率和内阻的实验技术。对于测量电阻率，你必须使用千分尺测量金属丝直径的多个位置以考虑厚度均匀性，并计算平均面积。评分标准奖励提及使用千分尺螺旋测微计，因为其测量精度为0.01 mm。对于长度，使用米尺，并从金属丝与夹子接触的点开始测量——而不是整个金属丝（如果使用鳄鱼夹）。
When measuring the I–V characteristic of a component, use a variable resistor as a potential divider to vary the voltage gradually, rather than a simple rheostat in series which cannot reduce the voltage to zero. The mark scheme also requires you to include a protective resistor for the diode to prevent a large current from damaging it. Always record both current and voltage readings and reverse the power supply to obtain the reverse characteristics for the diode.
在测量元件的I-V特性时，应该使用可变电阻器作为分压器来逐渐改变电压，而不是使用简单的串联变阻器（后者不能将电压降到零）。评分标准还要求为二极管加入保护电阻，以防止大电流损坏二极管。始终记录电流和电压读数，并反转电源以获得二极管的反向特性。
For the internal resistance experiment, you need a battery, an ammeter, a voltmeter and a variable resistor. Change the variable resistor and record pairs of I and V readings. The mark scheme emphasises that you should switch off the circuit between readings to prevent the battery from heating and changing its EMF. Also, take multiple readings and plot a graph of V against I to improve accuracy.
对于内阻实验，你需要电池、电流表、电压表和可变电阻器。改变可变电阻器并记录I和V读数对。评分标准强调在两次读数之间应关闭电路，以防止电池发热并改变其电动势。同时，采集多组数据并绘制V-I图像以提高精度。
7. Internal Resistance and EMF – Concept and Calculation | 7. 内阻与电动势 – 概念与计算
The June 2019 mark scheme paid close attention to the distinction between EMF and terminal potential difference. EMF (E) is the energy supplied per unit charge by the source, while terminal p.d. (V) is the voltage across the terminals when current flows. The difference is the lost volts, equal to Ir. The mark scheme rewarded candidates who explained that the internal resistance causes the terminal p.d. to be less than the EMF when a current is drawn.
2019年6月的评分标准非常关注电动势与端电势差之间的区别。电动势（E）是电源每单位电荷提供的能量，而端电势差（V）是当有电流通过时电源两端的电压。两者的差值就是损耗电压，等于Ir。评分标准奖励那些解释内阻导致端电势差小于电动势（当有电流输出时）的考生。
Calculation questions often give a battery of EMF E and internal resistance r connected to an external resistor. The mark scheme expects you to first calculate the total resistance as R + r, then use I = E/(R + r). Then terminal p.d. is V = IR, or V = E – Ir. A common error is using E = I R without including r; the mark scheme penalises this omission. Always state the equation for total resistance before substitution.
计算题通常给出一个电动势E和内阻r的电池，并连接一个外部电阻。评分标准期望你先计算总电阻为R + r，然后使用I = E/(R + r)。然后端电势差为V = IR，或V = E – Ir。常见错误是使用E = I R而不包含r；评分标准会因此扣分。总在代入前写出总电阻的方程。
When asked to explain how internal resistance affects the brightness of a lamp or the output voltage of a power supply, refer to lost volts. As the current increases, the lost volts (I r) increase, so the terminal p.d. decreases. For a high supply current, the external voltage may drop significantly. The mark scheme awards a mark for identifying the relationship between terminal p.d. and internal resistance, and another mark for explaining the consequence for the circuit.
当被要求解释内阻如何影响灯泡亮度或电源的输出电压时，应提及损耗电压。随着电流增大，损耗电压（I r）增大，因此端电势差减小。对于高电流输出，外部电压可能显著下降。评分标准为识别端电势差与内阻之间的关系给1分，为解释对电路的影响再给1分。
8. Common Mark Scheme Penalties – How to Avoid Losing Marks | 8. 常见评分扣分点 – 如何避免失分
The June 2019 examiner’s report (based on the mark scheme) identified several common errors. One of the most frequent was mixing up units: writing volts for resistance, or omitting the unit entirely. The mark scheme only awards the final mark if the unit is correct. For example, if you calculate resistivity and give an answer of 1.7 × 10⁻⁸ without Ω m, you lose the unit mark. Always include units for every numerical answer, and check that they are the appropriate SI derived units.
2019年6月的考官报告（基于评分标准）指出了几个常见错误。最常见的是单位混淆：将伏特作为电阻的单位，或完全省略单位。评分标准只有在单位正确时才给最终答案分。例如，如果你计算出电阻率为1.7 × 10⁻⁸但没有Ω m，就会失去单位分。始终为每个数值答案包含单位，并检查它们是否为合适的SI导出单位。
Another penalty is incorrect significant figures. AQA mark schemes typically allow one significant figure above or below the specification. If the data is given to 3 significant figures, your answer should also be to 3 significant figures. Writing too many or too few significant figures can lose the “consistent significant figures” mark. The mark scheme for June 2019 specifically stated that answers with more than 3 significant figures were not accepted unless the third significant figure was zero.
另一个扣分点是有效数字不正确。AQA评分标准通常允许比规定值多或少一位有效数字。如果数据给出3位有效数字，你的答案也应为3位有效数字。过多或过少的有效数字可能会失去“一致有效数字”的分数。2019年6月的评分标准明确指出，超过3位有效数字的答案（除非第三位有效数字是零）不被接受。
In written answers, using the wrong physics term costs marks. For example, saying “voltage” instead of “potential difference”, or “current flow” instead of “current” is penalised. The mark scheme uses key terms such as “charge carriers”, “rate of flow”, “energy per unit charge”. Learn the specification’s precise language. Also, when a question says “state and explain”, you must provide both a statement of the fact and a reason. Missing the explanation loses at least half the marks.
在书面回答中，使用错误的物理术语会扣分。例如，说“voltage”而不是“potential difference”，或说“current flow”而不是“current”都会扣分。评分标准使用关键术语如“charge carriers”、“rate of flow”、“energy per unit charge”。学习大纲的精确语言。另外，当问题说“state and explain”时，你必须既要陈述事实又要给出理由。缺少解释至少会失去一半的分数。
9. Exam Technique – “Show That” and “Explain” Questions | 9. 答题技巧 – “证明”与“解释”类问题
“Show that” questions are common in the AQA AS papers. In June 2019, a typical question asked candidates to show that the resistance of a wire is around a certain value. The mark scheme requires you to show your working with at least two steps. You should write the equation, substitute values (usually in standard form), and give the result to an appropriate number of significant figures. If you simply give the value without working, you cannot receive the method mark, which is usually the only mark for the question.
“Show that”问题在AQA AS试卷中很常见。在2019年6月，一个典型问题要求考生证明某个金属丝的电阻约为某个值。评分标准要求你展示至少两步的运算过程。你应该写出方程、代入数值（通常以标准形式），并给出适当的有效数字结果。如果你只给出数值而不写过程，则无法获得方法分（通常是该题唯一的分数）。
For “explain” questions, the mark scheme uses a ticks-based approach: each correct point earns one mark. A good explanation typically has three parts: a physics principle, a cause-and-effect link, and a conclusion. For example, “As temperature increases, the average kinetic energy of charge carriers increases, so they collide more frequently with the lattice, meaning the mean drift velocity decreases for a given current, hence the resistance increases.” The mark scheme awards separate marks for each highlighted phrase, so do not write a single long sentence; break it into shorter points.
对于“解释”类问题，评分标准使用打勾的方式：每个正确的要点得1分。一个好的解释通常有三部分：物理原理、因果关系链和结论。例如：“随着温度升高，载流子的平均动能增加，因此它们与晶格的碰撞更加频繁，这意味着在给定电流下平均漂移速度减小，因此电阻增加。”评分标准为每个加粗短语单独给分，所以不要写一个很长的句子；将其分解为较短的要点。
Always read the command word carefully: “Calculate” expects a numerical answer; “State” expects a one-word or one-line answer; “Suggest” allows you to use your own reasoning; “Determine” often requires a graph or calculation. The June 2019 mark scheme showed that too many candidates wrote long answers for a “State” question, wasting time and making careless mistakes. Match the length of your answer to the number of marks allocated, and keep it concise and precise.
始终仔细阅读指令词：“Calculate”期望数值答案；“State”期望一个词或一句话的答案；“Suggest”允许你使用自己的推理；“Determine”通常需要图像或计算。2019年6月的评分标准显示，太多考生为“State”问题写了长篇大论，浪费时间且犯粗心错误。让你的答案长度与分数匹配，并保持简洁精确。
10. Using Mark Schemes for Revision – A Strategic Approach | 10. 使用评分标准进行复习 – 策略方法
To benefit most from the June 2019 mark scheme, do not just read it passively. Instead, attempt the paper under timed conditions,
Published by TutorHao | AS Physics Revision Series | aleveler.com
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