📚 Electric Circuits and Magnetism | 电路与磁
Electric circuits transfer energy from a power source to components such as bulbs, resistors and motors. Understanding current, voltage and resistance helps scientists predict how a circuit behaves, while magnetism explains how moving charges create force fields and how electromagnets are made.
电路将能量从电源传递到灯泡、电阻器和电动机等元件。理解电流、电压和电阻有助于科学家预测电路的行为，而磁学解释了运动电荷如何产生力场以及电磁铁是如何制成的。
1. Electric Charge and Current | 电荷与电流
Electric current is the rate of flow of electric charge. In a metal wire, the moving charges are free electrons, while in an electrolyte, positive and negative ions both carry charge.
电流是电荷流动的速率。在金属导线中，移动的电荷是自由电子，而在电解质中，正离子和负离子都携带电荷。
Current is measured in amperes (A) using an ammeter connected in series. One ampere is the flow of one coulomb of charge per second, as shown below.
电流以安培（A）为单位，用串联在电路中的电流表测量。1 安培表示每秒有 1 库仑的电荷流过，如下式所示。
I = Q ÷ t
Conventional current flows from the positive terminal to the negative terminal of a cell, opposite to the direction of electron flow.
传统电流从电池正极流向负极，与电子的流动方向相反。
2. Voltage and Potential Difference | 电压与电势差
Voltage, also called potential difference, measures the energy transferred per unit charge between two points in a circuit. A higher voltage means each coulomb of charge carries more energy.
电压，也称为电势差，测量电路中两点之间每单位电荷转移的能量。电压越高，每库仑电荷携带的能量越多。
Voltage is measured in volts (V) using a voltmeter connected in parallel across a component. The relationship between energy, charge and voltage is:
电压以伏特（V）为单位，使用并联在元件两端的电压表测量。能量、电荷和电压之间的关系为：
V = E ÷ Q
A cell or battery provides the voltage that pushes charge around a complete circuit. Without a complete loop, charge cannot flow steadily and components will not work.
电池或电池组提供推动电荷在完整回路中流动的电压。如果没有完整的回路，电荷就无法持续流动，元件也不会工作。
3. Resistance and Ohm’s Law | 电阻与欧姆定律
Resistance is a measure of how much a component opposes the flow of electric current. It is measured in ohms (Ω). A long, thin wire has greater resistance than a short, thick wire of the same material.
电阻是衡量元件对电流阻碍作用的量，单位为欧姆（Ω）。相同材料的长而细的导线比短而粗的导线电阻更大。
For a metallic conductor at constant temperature, the current through it is directly proportional to the voltage across it. This is known as Ohm’s law:
对于温度恒定的金属导体，通过它的电流与其两端的电压成正比。这就是欧姆定律：
V = I × R
Because current and voltage are proportional, doubling the voltage across a fixed resistor doubles the current through it, as long as the temperature remains constant.
由于电流与电压成正比，只要温度保持不变，将固定电阻两端的电压加倍，通过它的电流也会加倍。
4. Series Circuits | 串联电路
In a series circuit, components are connected one after another in a single loop. The same current flows through every component because there is only one path for charge.
在串联电路中，元件一个接一个地连接成单一回路。由于电荷只有一条路径，因此每个元件中流过的电流相同。
The total resistance of resistors in series is the sum of their individual resistances:
串联电阻的总电阻等于各电阻之和：
Rₜ = R₁ + R₂ + R₃
If one component in a series circuit breaks or is removed, the whole circuit stops working because the single loop is broken.
如果串联电路中的一个元件损坏或被移除，整个电路都会停止工作，因为唯一的回路被切断了。
5. Parallel Circuits | 并联电路
In a parallel circuit, components are connected on separate branches between the same two points. The voltage across each branch is the same as the supply voltage.
在并联电路中，元件连接在相同两点之间的不同支路上。每条支路两端的电压与电源电压相同。
The total current from the supply is the sum of the currents in all branches. The total resistance of two resistors in parallel is less than the resistance of the smallest resistor. The formula for two resistors is:
电源输出的总电流等于各支路电流之和。两个并联电阻的总电阻小于其中最小的电阻。两个电阻的并联公式为：
1 ÷ Rₜ = 1 ÷ R₁ + 1 ÷ R₂
| Series | 串联 | Parallel | 并联 |
| Same current | 电流相同 | Same voltage per branch | 各支路电压相同 |
| Voltages add up | 电压相加 | Currents add up | 电流相加 |
| One break stops all | 一处断开全部停止 | 更多咨询请联系16621398022（同微信）
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