📚 IGCSE Physics: Calculating Resistance and Factors Affecting It | IGCSE物理：电阻的计算与影响因素
Resistance is one of the most important concepts in electrical circuits. For IGCSE Physics, you need to not only calculate resistance using Ohm’s law but also understand how the shape, material and temperature of a conductor affect its resistance. This article explains these ideas step by step, with worked examples and exam-style tips.
电阻是电路中最核心的概念之一。对于IGCSE物理，你不仅需要会用欧姆定律计算电阻，还要理解导体的形状、材料和温度如何影响其电阻。本文将逐步解释这些概念，并提供例题和考试技巧。
1. What is Resistance? | 什么是电阻？
Resistance measures how much a component opposes the flow of electric current. When electrons move through a conductor, they collide with the fixed positive ions in the material. These collisions transfer energy and slow down the flow, creating resistance.
电阻衡量元件对电流流动的阻碍程度。当电子通过导体时，会与材料中固定的正离子碰撞。这些碰撞会传递能量并阻碍流动，从而产生电阻。
Resistance is defined as the ratio of the potential difference across a component to the current flowing through it:
电阻定义为元件两端的电势差与通过它的电流之比：
R = V / I
where R is resistance measured in ohms (Ω), V is potential difference in volts (V), and I is current in amperes (A). One ohm is equal to one volt per ampere: 1 Ω = 1 V / A.
其中 R 是电阻，单位欧姆（Ω）；V 是电势差，单位伏特（V）；I 是电流，单位安培（A）。1欧姆等于1伏特每安培：1 Ω = 1 V / A。
2. Ohm’s Law and Calculating Resistance | 欧姆定律与电阻计算
Ohm’s law applies to metal conductors at constant temperature. It states that the current through a conductor is directly proportional to the potential difference across it, provided the physical conditions, especially temperature, do not change. This means the resistance stays constant.
欧姆定律适用于恒定温度下的金属导体。它指出，在物理条件（尤其是温度）不变的情况下，通过导体的电流与导体两端的电势差成正比。这意味着电阻保持不变。
Ohm’s law is normally written as:
欧姆定律通常写作：
V = I × R
To find resistance, rearrange the equation:
为求电阻，重排该方程：
R = V / I
In a circuit, place an ammeter in series to measure current and a voltmeter in parallel to measure voltage. Then divide the voltage reading by the current reading to get the resistance of the component.
在电路中，将电流表串联在电路中测量电流，将电压表并联在元件两端测量电压，然后用电压读数除以电流读数即可得到该元件的电阻。
For example, if a reading shows 3 V across a resistor and 0.5 A through it, the resistance is R = 3 V ÷ 0.5 A = 6 Ω.
例如，若测得电阻两端电压为3 V，电流为0.5 A，则电阻为 R = 3 V ÷ 0.5 A = 6 Ω。
3. Resistivity and Material | 电阻率与材料
Different materials have different abilities to conduct electricity. Metals like copper and silver have low resistance, so they are used for cables. Materials like rubber and plastic have very high resistance and are used as insulators. The fundamental property that describes how strongly a material resists current is its resistivity (ρ).
不同材料的导电能力不同。铜、银等金属电阻低，因此用作导线。橡胶、塑料等材料电阻非常高，用作绝缘体。描述材料对电流阻碍程度的基本属性称为电阻率（ρ）。
For a uniform wire, resistance is related to resistivity, length and cross-sectional area by this formula:
对于均匀导线，电阻与电阻率、长度和横截面积的关系如下：
R = ρL / A
where ρ is the resistivity in ohm-metres (Ω·m), L is the length in metres (m), and A is the cross-sectional area in square metres (m²).
其中 ρ 是电阻率，单位欧姆·米（Ω·m）；L 是长度，单位米（m）；A 是横截面积，单位平方米（m²）。
For example, copper has a very low resistivity (about 1.7 × 10⁻⁸ Ω·m), so it is an excellent conductor. Nichrome has a much higher resistivity and is used in heating elements.
例如，铜的电阻率非常低（约1.7 × 10⁻⁸ Ω·m），是优良导体。镍铬合金电阻率高得多，常用于电热元件。
4. Effect
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