📚 AS AQA Physics: Electricity | AS AQA 物理：电学
Electricity is a core topic in AS AQA Physics. This revision guide covers the key definitions, laws, and circuit techniques you need for your OxfordAQ A AS Level examination.
电学是 AS AQA 物理的核心主题。本复习指南涵盖了牛津AQA AS 水平考试所需的关键定义、定律和电路技巧。
1. Electric Current and Charge | 电流与电荷
e. For a steady current, the charge ΔQ passing a point in a time Δt is given by I = ΔQ/Δt.
电流定义为电荷流动的速率。对于恒定电流，在时间 Δt 内通过某一点的电荷量 ΔQ 由 I = ΔQ/Δt 给出。
I = ΔQ/Δt
The unit of current is the ampere (A), and the unit of charge is the coulomb (C). One ampere is one coulomb per second.
电流的单位是安培（A），电荷的单位是库仑（C）。1 安培等于 1 库仑每秒。
In metals, charge is carried by free electrons. In electrolytes, both positive and negative ions carry charge.
在金属中，电荷由自由电子携带。在电解液中，正离子和负离子都携带电荷。
The ammeter is used to measure current and must be placed in series with the component.
安培表用于测量电流，必须与元件串联连接。
charge e = 1.60 × 10⁻¹⁹ C. Total charge Q = ne, where n is the number of charge carriers.
元电荷 e = 1.60 × 10⁻¹⁹ C。总电荷 Q = ne，其中 n 是电荷载流子的数量。
2. Voltage and Energy | 电压与能量
charge between two points in a circuit. It is measured in volts (V), where 1 V = 1 J C⁻¹.
电压（电势差）是电路中两点间单位电荷所转移的能量。单位是伏特（V），1 V = 1 J C⁻¹。
V = W/Q
Here, W is the energy transferred (in joules) and Q is the charge (in coulombs). The voltage across a component indicates how much electrical energy is converted into other forms, such as heat or light.
其中 W 是转移的能量（单位：焦耳），Q 是电荷（单位：库仑）。元件两端的电压表示有多少电能被转化为其他形式，例如热或光。
A voltmeter is always connected in parallel across a component to measure the p.d.
电压表总是与元件并联以测量电势差。
The potential difference across a battery when no current flows is called the electromotive force (EMF). More detail is given in Section 8.
当没有电流流过时，电池两端的电势差称为电动势（EMF）。详见第 8 节。
3. Resistance and Ohm's Law | 电阻与欧姆定律
Resistance is a measure of how a component opposes the flow of charge. It is defined by Ohm's law: the current through an ohmic conductor is directly proportional to the potential difference across it, provided temperature remains constant.
电阻是衡量元件阻碍电荷流动程度的物理量。欧姆定律定义为：对于欧姆导体，在温度保持不变的条件下，通过导体的电流与两端电势差成正比。
R = V/I
tor obeys this relationship; a graph of I against V is a straight line through the origin.
电阻的单位是欧姆（Ω），1 Ω = 1 V A⁻¹。欧姆导体满足该关系；I 随 V 变化的图像是一条过原点的直线。
Resistance depends on the material, length, and cross-sectional area of a conductor.
电阻取决于导体的材料、长度和横截面积。
A resistor is an intentional component with a fixed resistance. A rheostat is a variable resistor used to control current.
电阻器是具有固定电阻的元件。变阻器是用于控制电流的可变电阻器。
R = V/I is constant for an ohmic conductor. Non-ohmic devices have a changing resistance.
在恒定温度下，对于欧姆导体，R = V/I 为常数。非欧姆器件的电阻会发生变化。
4. Resistivity and Conductivity | 电阻率与电导率
Resistivity (ρ) is a material property that describes how strongly it opposes the flow of charge. It is defined by the equation:
电阻率（ρ）是描述材料对电荷流动阻碍程度的材料属性。其定义方程为：
R = ρL/A
where R is resistance, L is the length of the conductor, and A is its cross-sectional area. The SI unit of resistivity is the ohm-metre (Ω m).
其中 R 是电阻，L 是导体的长度，A 是导体的横截面积。电阻率的 SI 单位是欧姆·米（Ω m）。
tivity σ is the reciprocal of resistivity: σ = 1/ρ, measured in siemens per metre (S m⁻¹).
电导率 σ 是电阻率的倒数：σ = 1/ρ，单位为西门子每米（S m⁻¹）。
Metals have low resistivity (good conductors); insulators have very high resistivity.
金属具有低电阻率（良导体）；绝缘体具有极高的电阻率。
For a wire of constant cross-section, resistance increases linearly with length and decreases with increasing area.
对于横截面恒定的导线，电阻随长度线性增加，并随面积增大而减小。
5. I-V Characteristics | I-V 特性曲线
The I-V characteristic shows how the current through a component varies with the p.d. across it. Different components have different shapes.
I-V 特性曲线展示了元件两端电势差如何改变通过它的电流。不同元件具有不同形状的曲线。
Ohmic resistor: A straight line through the origin, showing constant resistance.
欧姆电阻器：一条过原点的直线，表明电阻恒定。
Filament lamp: The curve bends as current increases because the filament heats up, increasing resistance. The graph is not a straight line; the gradient decreases at higher voltages.
钨丝灯泡：随着电流增大，灯丝温度升高，电阻增大，因此曲线弯曲。图像不是直线，在高电压下斜率减小。
Semiconductor diode: Current only flows in one direction (forward bias) after a small threshold voltage (about 0.6 V for silicon). In reverse bias, current is essentially zero.
半导体二极管：电流仅在正向偏置时，电压超过阈值（硅约为 0.6 V）后才能流动。在反向偏置时，电流基本为零。
For a filament lamp: R increases as temperature increases
For a diode: reverse current is negligible
6. Series and Parallel Circuits | 串联与并联电路
In a series circuit, components are connected end-to-end, so the same current flows through each component. The total p.d. is the sum of the individual p.d.s, and the total resistance is the sum of all resistances.
在串联电路中，元件首尾相连，因此通过每个元件的电流相同。总电势差等于各个电势差之和，总电阻等于所有电阻之和。
Rtotal = R₁ + R₂ + R₃ + ...
In a parallel circuit, components are connected across the same two points, so the p.d. across each branch is the same. The total current is the sum of the branch currents, and the total resistance is found from:
在并联电路中，元件连接在同一对节点之间，因此每个支路两端的电势差相同。总电流等于各支路电流之和，总电阻由下式给出：
1/Rtotal = 1/R₁ + 1/R₂ + 1/R₃ + ...
Series circuits are used for potential dividers and where a common current is required.
串联电路用于分压器以及需要相同电流的场合。
Parallel circuits are used in household wiring, so each appliance operates at the same voltage.
并联电路用于家庭布线，使每个电器都在同一电压下工作。
Adding a resistor in parallel always decreases the total resistance, while adding in series always increases it.
并联增加电阻总使总电阻减小，而串联增加则总使总电阻增大。
7. Potential Divider | 电位分压器（分压电路）
A potential divider consists of two or more resistors in series across a supply voltage. It can provide a desired output voltage across one of the resistors.
电位分压器由两个或多个串联电阻组成，跨接在电源电压上。它可以在其中一个电阻两端提供所需的输出电压。
Vout = Vin × R₂/(R₁ + R₂)
where R₂ is the resistor across which the output voltage is taken. This equation assumes no load is connected to the output.
其中 R₂ 是取输出电压的电阻。该方程假设输出端没有连接负载。
If a load is connected in parallel with R₂, the effective resistance of that branch decreases, altering the output voltage.
如果在 R₂ 两端并联一个负载，该支路的等效电阻减小，从而改变输出电压。
Potential dividers are used in sensing circuits, such as light-dependent resistors (LDRs) and thermistors, where resistance changes with light or temperature.
电位分压器用于传感电路，例如光敏电阻（LDR）和热敏电阻，它们的电阻随光强或温度变化。
For a variable resistor (potentiometer), the output voltage can be continuously adjusted from 0 to Vin.
对于可变电阻（电位器），输出电压可以在 0 到 Vin 之间连续调节。
8. EMF and Internal Resistance | 电动势与内阻
The electromotive force (EMF, ε) of a source is the total energy supplied per unit charge. It is measured in volts and is equal to the p.d. across the source when no current flows.
电源的电动势（ε）是单位电荷所获得的总能量。单位为伏特，等于无电流通过时电源两端的电势差。
A real source has an internal resistance r. When current I flows, the terminal p.d. V is less than the EMF because energy is lost inside the source.
实际电源具有内阻 r。当电流 I 流动时，端电压 V 小于电动势，因为能量在电源内部有损失。
ε = I(R + r) = V + Ir
R is the external load resistance and V = IR is the potential difference across the load.
其中 R 是外部负载电阻，V = IR 是负载两端的电势差。
When the external resistance is infinite (open circuit), I = 0 and V = ε.
当外部电阻为无穷大（开路）时，I = 0，V = ε。
When the external resistance is zero (short circuit), the current is Imax = ε/r.
当外部电阻为零（短路）时，电流为 Imax = ε/r。
The maximum power is delivered to the load when R = r (for DC circuits).
当 R = r 时（对直流电路），负载获得最大功率。
9. Power and Energy in Circuits | 电路中的功率与能量
Power is the rate at which energy is transferred. In an electrical circuit, the power dissipated by a component is the product of the p.d. across it and the current through it.
功率是能量转移的速率。在电路中，元件消耗的功率等于其两端电势差与通过电流的乘积。
P = VI
Using Ohm's law, we can also write:
利用欧姆定律，我们还可以写出：
P = I²R = V²/R
Electrical energy transferred is given by:
转移的电能由下式给出：
W = VIt
where t is the time in seconds. The unit of energy is the joule (J).
其中 t 是以秒为单位的时间。能量的单位是焦耳（J）。
by each resistor is proportional to its resistance (P = I²R) because current is the same.
在串联电路中，由于电流相同，每个电阻消耗的功率与其电阻成正比（P = I²R）。
it, the power is inversely proportional to resistance (P = V²/R) because p.d. is the same.
在并联电路中，由于电势差相同，功率与电阻成反比（P = V²/R）。
Electrical appliances usually state their power rating and operating voltage, from which their resistance can be calculated.
电器通常标明其额定功率和工作电压，由此可以计算其电阻。
10. Conservation of Charge and Energy in Circuits | 电路中的电荷与能量守恒
Two fundamental principles govern all circuits:
两条基本原理支配着所有电路：
Conservation of charge: The total current entering a junction equals the total current leaving it (Kirchhoff's current law). This is why the current is the same in series and splits in parallel.
电荷守恒：流入节点的总电流等于流出节点的总电流（基尔霍夫电流定律）。这就是串联电路中电流相同、并联电路中电流分流的原因。
Conservation of energy: The algebraic sum of the EMFs and potential differences around any closed loop is zero (Kirchhoff's voltage law). This is why the sum of p.d.s in a series circuit equals the supply voltage.
能量守恒：沿任一闭合回路，电动势与电势差的代数和为零（基尔霍夫电压定律）。这就是串联电路中各电势差之和等于电源电压的原因。
These principles allow complex circuits to be analysed systematically, whether for exam problems or real-world diagnostics.
这些原理使得复杂电路可以被系统地分析，无论是用于考题还是实际故障诊断。
Summary | 总结
Mastering electricity in AS AQA Physics requires a solid grasp of definitions, the ability to apply Ohm's law and power equations, and familiarity with circuit configurations. Always draw clear circuit diagrams and label units correctly.
掌握 AS AQA 物理中的电学，需要扎实理解定义、能够应用欧姆定律和功率方程，并熟悉电路连接方式。始终画出清晰的电路图，并正确标注单位。
Use the formulas I = Q/t, V = W/Q, R = V/I, ρ = RA/L.
使用公式 I = Q/t、V = W/Q、R = V/I、ρ = RA/L。
Remember series and parallel resistance rules.
记住串联和并联电阻规则。
For EMF and internal resistance, use ε = V + Ir.
对于电动势和内阻，使用 ε = V + Ir。
Practise sketching I-V curves for ohmic conductors, lamps, and diodes.
练习绘制欧姆导体、灯泡和二极管的 I-V 曲线。
Published by TutorHao | Physics Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
或截图后用「扫一扫 → 相册」选择本图