📚 A-Level AQA Physics: Resistance – Key Concepts Explained | A-Level AQA物理：电阻考点精讲
Resistance is a fundamental concept in AQA A-level Physics that governs how electrical components behave in circuits. Mastering this topic is essential for tackling both theoretical questions and practical investigations in the current electricity module.
电阻是AQA A-level物理中的一个基本概念，它决定了电路元件在电路中的行为。掌握这一主题对于应对电流电学模块中的理论问题和实验探究题至关重要。
1. What is Resistance? Ohm’s Law | 什么是电阻？欧姆定律
Resistance (R) is a measure of the opposition to current flow. It is defined by the equation R = V/I, where V is the potential difference across the component and I is the current through it. The SI unit is the ohm (Ω).
电阻(R)是对电流阻碍作用的量度。由公式R = V/I定义，其中V是元件两端的电势差，I是通过的电流。SI单位是欧姆(Ω)。
R = V / I
Ohm’s law states that, for a metallic conductor at constant temperature, the current is directly proportional to the potential difference. This means the resistance remains constant; such a conductor is described as ohmic.
欧姆定律指出，对于恒定温度下的金属导体，电流与电势差成正比。这意味着电阻保持恒定；这样的导体称为欧姆导体。
An I-V graph for an ohmic conductor is a straight line passing through the origin, with gradient equal to 1/R (or R from V/I).
欧姆导体的I-V特性图是一条通过原点的直线，斜率等于1/R（或通过V/I求得R）。
2. Resistivity and the Resistance Formula | 电阻率与电阻公式
The resistance of a uniform wire depends on its length L, cross-sectional area A, and the material’s resistivity ρ. The relationship is R = ρL/A. Resistivity is an intrinsic property measured in ohm-metres (Ω·m). Good conductors have low resistivity.
均匀导线的电阻取决于其长度L、截面积A和材料的电阻率ρ。关系式为R = ρL/A。电阻率是材料的固有属性，单位为欧姆·米(Ω·m)。良导体的电阻率很低。
R = ρL / A
Resistivity changes with temperature; for metals, ρ increases as temperature rises because more lattice vibrations scatter electrons.
电阻率随温度变化；对于金属，温度升高时ρ增大，因为更多的晶格振动散射电子。
3. Temperature Effects on Resistance | 温度对电阻的影响
In metallic conductors, increasing temperature causes increased atomic vibrations, which hinder the flow of electrons, so resistance rises. The temperature coefficient of resistance α is positive.
在金属导体中，温度升高导致原子振动加剧，阻碍电子流动，因此电阻增大。电阻的温度系数α为正。
A negative temperature coefficient (NTC) thermistor shows a dramatic decrease in resistance as temperature increases. This makes it useful in temperature-sensing circuits.
负温度系数(NTC)热敏电阻在温度升高时电阻显著下降。这使得它可用于温度传感电路。
Superconductivity is a phenomenon where certain materials exhibit zero resistivity below a critical temperature (Tc). Once in the superconducting state, they can carry current without energy loss. Key metals and ceramics become superconductors at very low temperatures. Research aims to find room-temperature superconductors.
超导是一种现象，某些材料在临界温度(Tc)以下电阻率为零。一旦进入超导态，它们可以无能量损耗地承载电流。一些金属和陶瓷在极低温度下成为超导体。研究致力于寻找室温超导体。
R = 0 for T < Tc
4. I-V Characteristics of Key Components | 关键元件的I-V特性
The I-V characteristic of a metallic conductor at constant temperature is a straight line through the origin, consistent with Ohm’s law.
恒温下金属导体的I-V特性是通过原点的直线，符合欧姆定律。
A filament lamp has a wire that heats up as current increases. Its resistance increases with temperature, causing the I-V graph to curve – showing a decreasing gradient as p.d. increases. The characteristic is symmetrical for positive and negative voltages.
白炽灯的灯丝随着电流增加而发热。其电阻随温度升高而增大，使得I-V曲线弯曲——随着电压增大斜率减小。该特性对正负电压对称。
A semiconductor diode only conducts when forward biased (above approximately 0.6 V for silicon). In reverse bias, virtually no current flows until breakdown. The I-V graph shows a sharp rise in current after the threshold voltage, and nearly zero current for reverse voltages.
半导体二极管只有在正向偏置（硅管约0.6V以上）时导通。反向偏置时几乎没有电流，直到击穿。I-V图显示在阈值电压后电流急剧上升，而反向电压下电流几乎为零。
5. Thermistors and LDRs in Depth | 深入理解热敏电阻和光敏电阻
Thermistors (NTC type) have a resistance that decreases exponentially with increasing temperature. They are often used in potential divider circuits to produce a voltage that varies with temperature, e.g. in a thermostat or fire alarm.
热敏电阻（NTC型）的电阻随温度升高呈指数下降。它们常用于分压电路，产生随温度变化的电压，例如用于恒温器或火灾报警器。
Light-dependent resistors (LDRs) show a decrease in resistance as the light intensity increases. In darkness, resistance is very high (megohms); in bright light, it falls dramatically (few hundred ohms). LDRs are used in automatic lighting and burglar alarms.
光敏电阻(LDR)的电阻随光照强度增加而降低。黑暗中电阻很高（兆欧级）；强光下显著下降（几百欧）。LDR用于自动照明和防盗报警器。
6. Resistors in Series and Parallel | 电阻的串联与并联
When resistors are connected in series, the total (equivalent) resistance is the sum of individual resistances. This is because the same current passes through each resistor, and the total p.d. is the sum of individual p.d.s.
当电阻串联时，总（等效）电阻为各电阻之和。这是因为各电阻中通过相同电流，总电压为各电压之和。
Rtotal = R₁ + R₂ + …
For parallel resistors, the reciprocal of the total resistance equals the sum of reciprocals. The total resistance is always less than the smallest individual resistance. The potential difference is the same across each branch.
对于并联电阻，总电阻的倒数等于各电阻倒数之和。总电阻总是小于最小的单个电阻。每个支路两端的电压相等。
1/Rtotal = 1/R₁ + 1/R₂ + …
7. Internal Resistance of a Source | 电源的内阻
All real power supplies (batteries, cells) have some internal resistance r. The electromotive force (e.m.f.) ε is the energy transferred per unit charge when no current flows. When current I flows, the terminal p.d. V is given by V = ε – Ir.
所有实际电源（电池、电池组）都有一定的内阻r。电动势(ε)是无电流流动时每单位电荷转换的能量。当有电流I流动时，端电压V由V = ε – Ir给出。
V = ε – Ir
The lost volts (Ir) increase with current. A graph of terminal p.d. against current yields a straight line with gradient –r and intercept ε. This is used in the standard experiment to determine internal resistance.
损失的电压(Ir)随电流增大。端电压对电流的图线是一条斜率为–r、截距为ε的直线。这用于测量内阻的标准实验。
8. Potential Dividers and Potentiometers | 分压器与电位器
A potential divider uses two (or more) resistors in series to produce a fraction of the input voltage. The output voltage Vout across a resistor R₂ is derived from the fact that current is the same and V = IR.
分压器利用两个（或多个）串联电阻，产生输入电压的一部分。电阻R₂两端的输出电压Vout源于电流相同且V=IR。
Vout = (R₂ / (R₁ + R₂)) · Vin
A potentiometer is a variable potential divider with three terminals. It can provide a continuously adjustable output voltage, often used to calibrate sensors or control circuits. If one resistor in a divider is a
Published by TutorHao | A-Level Physics Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
屏轩国际教育cambridge primary/secondary checkpoint, cat4, ukiset,ukcat,igcse,alevel,PAT,STEP,MAT, ibdp,ap,ssat,sat,sat2课程辅导，国外大学本科硕士研究生博士课程论文辅导