📚 IGCSE WJEC Science: Calculation Skills Masterclass | IGCSE WJEC 科学：计算题专项训练
Calculation questions form a major part of the WJEC IGCSE Science assessments, testing your ability to apply mathematical skills in Physics, Chemistry and Biology contexts. This article covers the essential formulas, techniques and worked examples you need to master for the exams.
计算题是 WJEC IGCSE 科学考试的重要组成部分，考查你在物理、化学和生物学情境中应用数学技能的能力。本文涵盖了你需要精通的基本公式、解题技巧和典型例题，帮助你备战考试。
1. Units and Conversions | 单位与换算
Always check the units given in the question. Common conversions include kilograms to grams (1 kg = 1000 g), centimetres to metres (1 m = 100 cm), and minutes to seconds (1 min = 60 s). In calculations, you must use SI units for accurate results.
始终核对题目所给的单位。常见的换算包括千克与克 (1 kg = 1000 g)，厘米与米 (1 m = 100 cm)，分钟与秒 (1 min = 60 s)。在计算中，必须使用国际单位制 (SI) 才能得到准确结果。
Example: Convert 5400 cm to metres → 5400 ÷ 100 = 54 m
示例：将 5400 厘米转换为米 → 5400 ÷ 100 = 54 m
2. Speed, Distance and Time | 速度、距离与时间
The relationship is given by speed = distance ÷ time. Rearranging gives distance = speed × time and time = distance ÷ speed. Typical units are m/s for speed, metres for distance and seconds for time.
基本关系为 速度 = 距离 ÷ 时间。经移项可得 距离 = 速度 × 时间，以及 时间 = 距离 ÷ 速度。速度通常以 m/s、距离以米、时间以秒为单位。
A car travels 150 km in 2 hours. Calculate its average speed in km/h. → Speed = 150 ÷ 2 = 75 km/h.
一辆汽车在 2 小时内行驶 150 公里。计算其平均速度 (km/h)。→ 速度 = 150 ÷ 2 = 75 km/h。
3. Acceleration | 加速度
Acceleration is the rate of change of velocity: a = (v – u) ÷ t, where v is final velocity, u is initial velocity and t is the time taken. The unit is m/s². Deceleration is negative acceleration.
加速度是速度的变化率：a = (v – u) ÷ t，其中 v 为末速度，u 为初速度，t 为所用时间。单位为 m/s²。减速即为负加速度。
A cyclist increases velocity from 4 m/s to 10 m/s in 3 seconds. Find acceleration. → a = (10 – 4) ÷ 3 = 2 m/s².
一名自行车手在 3 秒内将速度从 4 m/s 提升到 10 m/s，求加速度。→ a = (10 – 4) ÷ 3 = 2 m/s²。
4. Force and Newton’s Second Law | 力与牛顿第二定律
Force (N) = mass (kg) × acceleration (m/s²). This is often used with weight: weight (N) = mass (kg) × gravitational field strength (N/kg). Remember 1 N is the force needed to accelerate 1 kg at 1 m/s².
力 (N) = 质量 (kg) × 加速度 (m/s²)。这一定律常与重力结合：重力 (N) = 质量 (kg) × 重力场强度 (N/kg)。记住 1 N 是使 1 kg 物体产生 1 m/s² 加速度所需的力。
What force is needed to accelerate a 1200 kg car at 3 m/s²? → F = 1200 × 3 = 3600 N.
要使 1200 kg 的汽车以 3 m/s² 的加速度行驶，需要多大的力？→ F = 1200 × 3 = 3600 N。
5. Work Done and Energy | 做功与能量
Work done (J) = force (N) × distance moved in the direction of the force (m). This equation also applies to gravitational potential energy: GPE = mgh, where g is gravitational field strength and h is height.
做功 (J) = 力 (N) × 沿力的方向移动的距离 (m)。该公式也用于重力势能：GPE = mgh，其中 g 为重力场强度，h 为高度。
How much work is done lifting a 20 kg box through a height of 2 m? (g = 10 N/kg) → Force = weight = 20 × 10 = 200 N, work = 200 × 2 = 400 J.
将一个 20 kg 的箱子提升 2 m，做了多少功？(g = 10 N/kg) → 力 = 重力 = 20 × 10 = 200 N，功 = 200 × 2 = 400 J。
6. Power | 功率
Power (W) = work done (J) ÷ time (s) or power = energy transferred ÷ time. 1 watt is 1 joule per second. In electrical contexts, P = I × V.
功率 (W) = 做功 (J) ÷ 时间 (s)，也可表示为 功率 = 转化能量 ÷ 时间。1 瓦特等于每秒 1 焦耳。在电学中，P = I × V。
An electric motor does 600 J of work in 12 s. Calculate its power. → P = 600 ÷ 12 = 50 W.
一台电动机在 12 秒内做功 600 J，计算其功率。→ P = 600 ÷ 12 = 50 W。
7. Ohm’s Law and Resistance | 欧姆定律与电阻
Resistance (Ω) = voltage (V) ÷ current (A). Rearrangements: V = I × R and I = V ÷ R. Remember that resistance is constant for an ohmic conductor at constant temperature.
电阻 (Ω) = 电压 (V) ÷ 电流 (A)。移项后得 V = I × R 和 I = V ÷ R。记住对于欧姆导体，在一定温度下电阻是恒定的。
A lamp has a current of 0.5 A when connected to a 6 V supply. Find its resistance. → R = 6 ÷ 0.5 = 12 Ω.
一盏灯接入 6 V 电源时电流为 0.5 A，求电阻。→ R = 6 ÷ 0.5 = 12 Ω。
8. Electrical Power and Energy | 电功率与电能
Electrical power can be calculated using P = I × V or P = I² × R. Energy transferred (J) = power (W) × time (s). Electricity bills use kilowatt-hours: E (kWh) = power (kW) × time (h).
电功率可用 P = I × V 或 P = I² × R 计算。转化电能 (J) = 功率 (W) × 时间 (s)。电费单常用千瓦时：电能 (kWh) = 功率 (kW) × 时间 (h)。
A 2 kW heater is used for 3 hours. Calculate the energy transferred in kWh. → E = 2 × 3 = 6 kWh.
一个 2 kW 的加热器使用 3 小时，计算转移的电能 (kWh)。→ E = 2 × 3 = 6 kWh。
9. Moles and Molar Mass | 摩尔与摩尔质量
Number of moles = mass (g) ÷ molar mass (g/mol). The molar mass is the relative formula mass (Mr) expressed in grams. Always use the periodic table to find atomic masses.
摩尔数 = 质量 (g) ÷ 摩尔质量 (g/mol)。摩尔质量是以克表示相对式量 (Mr)。始终用元素周期表查找原子质量。
Calculate the moles in 8 g of oxygen gas (O₂). Mr = 2 × 16 = 32, so moles = 8 ÷ 32 = 0.25 mol.
计算 8 g 氧气 (O₂) 的物质的量。Mr = 2 × 16 = 32，因此物质的量 = 8 ÷ 32 = 0.25 mol。
10. Concentration of Solutions | 溶液浓度
Concentration (mol/dm³) = amount of solute (mol) ÷ volume of solution (dm³). Alternatively, concentration (g/dm³) = mass of solute (g) ÷ volume (dm³). Remember 1 dm³ = 1000 cm³.
浓度 (mol/dm³) = 溶质的物质的量 (mol) ÷ 溶液体积 (dm³)。也可表示为浓度 (g/dm³) = 溶质质量 (g) ÷ 体积 (dm³)。记住 1 dm³ = 1000 cm³。
0.5 mol of sodium hydroxide is dissolved in 250 cm³ of water. Find concentration in mol/dm³. → 250 cm³ = 0.25 dm³, concentration = 0.5 ÷ 0.25 = 2 mol/dm³.
将 0.5 mol 氢氧化钠溶于 250 cm³ 水中，求浓度 (mol/dm³)。→ 250 cm³ = 0.25 dm³，浓度 = 0.5 ÷ 0.25 = 2 mol/dm³。
11. Reacting Masses and Percentage Yield | 反应质量与产率
Using balanced equations, you can calculate the theoretical mass of a product. Percentage yield = (actual mass ÷ theoretical mass) × 100%. Atom economy is also important: atom economy = (Mr of desired product ÷ total Mr of reactants) × 100%.
使用配平的方程式，可以计算产物的理论质量。百分产率 = (实际质量 ÷ 理论质量) × 100%。原子经济性也很重要：原子经济性 = (所需产物的 Mr ÷ 反应物总 Mr) × 100%。
If 2.5 g of copper is produced from a reaction with a theoretical yield of 3.2 g, find the percentage yield. → (2.5 ÷ 3.2) × 100% = 78.1%.
某反应实际生成铜 2.5 g，理论产率为 3.2 g，求百分产率。→ (2.5 ÷ 3.2) × 100% = 78.1%。
12. Magnification in Biology | 生物学中的放大倍率
Magnification = size of image ÷ actual size of specimen. Both measurements must be in the same unit. This formula often appears when using microscopes or interpreting scale bars.
放大倍率 = 图像尺寸 ÷ 标本实际大小。两个测量值必须单位一致。这个公式常出现在显微镜使用或比例尺解读的情境中。
An image of a cell has a diameter of 20 mm, but the real cell is 0.05 mm. Magnification = 20 ÷ 0.05 = ×400.
某细胞图像直径为 20 mm，实际细胞为 0.05 mm。放大倍率 = 20 ÷ 0.05 = ×400。
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