IGCSE CIE Physics: Circuit Analysis – Key Points | IGCSE CIE 物理：电路分析考点精讲

📚 IGCSE CIE Physics: Circuit Analysis – Key Points | IGCSE CIE 物理：电路分析考点精讲

Understanding circuit analysis is fundamental in IGCSE CIE Physics. This guide covers key concepts such as current, voltage, resistance, Ohm’s law, series and parallel circuits, potential dividers, internal resistance, and electrical power—all crucial for exam success.

理解电路分析是 IGCSE CIE 物理的基础。本指南涵盖电流、电压、电阻、欧姆定律、串并联电路、分压器、内阻和电功率等关键概念，都是考试成功的关键。

1. Circuit Symbols and Diagrams | 电路符号与原理图

Correctly drawing and interpreting circuit diagrams is a vital skill. Use a ruler and avoid gaps.

正确绘制和解读电路图是关键技能。使用直尺，避免留下断线。

Always connect the ammeter in series and the voltmeter in parallel.

电流表总是串联在电路中，电压表总是并联。

A diode allows current to flow in one direction only (forward bias). An LED emits light when forward biased.

二极管只允许单向电流通过（正向偏置）。LED 在正向偏置时发光。

A thermistor has resistance that decreases as temperature increases; an LDR (light-dependent resistor) has resistance that decreases as light intensity increases.

热敏电阻的阻值随温度升高而减小；光敏电阻（LDR）的阻值随光照强度增大而减小。

Know the standard symbols for a cell, battery, switch, resistor, variable resistor, lamp, diode, LED, ammeter, voltmeter, thermistor, LDR, fuse and earth.

要熟记下列标准电路符号：电池、开关、电阻、可变电阻、灯泡、二极管、发光二极管、电流表、电压表、热敏电阻、光敏电阻、熔断器和接地。

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2. Current and Charge | 电流与电荷

Electric current is the rate of flow of electric charge. It is given by I = Q / t, where I is current (A), Q is charge (C), and t is time (s).

电流是电荷流动的速率，公式为 I = Q / t，其中 I 是电流（安培，A），Q 是电荷（库仑，C），t 是时间（秒，s）。

I = Q / t

Conventional current flows from positive to negative, but electrons flow from negative to positive. In metallic conductors, current is due to the movement of free electrons.

常规电流从正极流向负极，但电子从负极流向正极。在金属导体中，电流由自由电子移动形成。

The ampere (A) is the SI unit of current; 1 A = 1 C/s. In an electric circuit, current is measured by an ammeter connected in series.

安培（A）是电流的国际单位，1 A = 1 C/s。在电路中，用串联的电流表测量电流。

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3. Voltage, Potential Difference and EMF | 电压、电势差与电动势

Potential difference (p.d.) is the work done per unit charge to move a charge between two points. It is measured in volts (V). 1 V = 1 J/C.

电势差（p.d.）是将单位电荷从一点移动到另一点所做的功，单位是伏特（V），1 V = 1 J/C。

V = W / Q

Electromotive force (EMF, ε) is the total energy supplied to each coulomb of charge by a source. It is not a force but a voltage.

电动势（EMF，记作 ε）是电源向每库仑电荷提供的总能量。它不是力，而是电压。

A voltmeter is always connected in parallel across the component to measure p.d. An ideal voltmeter has infinite resistance.

电压表总是并联在元件两端测量电势差。理想电压表的电阻无穷大。

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4. Resistance and Ohm’s Law | 电阻与欧姆定律

Resistance is the opposition to current flow. It is given by R = V / I, where R is resistance (Ω), V is p.d. (V), I is current (A).

电阻是对电流的阻碍作用。公式为 R = V / I，其中 R 是电阻（欧姆，Ω），V 是电势差（V），I 是电流（A）。

R = V / I

Ohm’s law states that, at constant temperature, the current through a conductor is directly proportional to the potential difference across it. Thus V = I R for ohmic conductors.

欧姆定律指出，在恒温下，通过导体的电流与导体两端的电势差成正比。因此对于欧姆导体，有 V = I R。

The resistance of a wire depends on its length, cross-sectional area, and material resistivity. Longer wires have greater resistance, and thicker wires have lower resistance.

导线的电阻取决于长度、截面积和材料的电阻率。导线越长电阻越大，导线越粗电阻越小。

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5. I–V Characteristics | 电流-电压特性曲线

The I–V graph of an ohmic resistor (at constant temperature) is a straight line through the origin, showing that current is proportional to voltage.

欧姆电阻（恒温）的 I-V 图是一条过原点的直线，表明电流与电压成正比。

For a filament lamp, the I–V curve is not a straight line: as current increases, the wire heats up, resistance increases, so the graph flattens.

对于白炽灯，I-V 曲线不是直线：随着电流增大，灯丝发热，电阻增大，因此曲线趋于平缓。

A diode has a very high resistance in reverse bias and a low resistance

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