📚 Current and Voltage | 电流与电压
Electric circuits need both current and voltage. Current is the flow of electric charge, while voltage is the push that drives the charge around a circuit. This article explains how to understand, measure and compare current and voltage in series and parallel circuits for KS3 CIE.
电路需要电流和电压。电流是电荷的流动，电压是推动电荷在电路中运动的“推力”。本文为 KS3 CIE 学生讲解如何理解、测量并比较串联和并联电路中的电流与电压。
1. Electric Charge and Current | 电荷与电流
In any electric circuit, we need moving charge. Metals contain free electrons that can move from atom to atom. When a cell or battery is connected into a complete circuit, it makes these electrons drift in one direction. This directed flow of electric charge is called an electric current. The more charge that passes a point in one second, the larger the current.
在任何电路中，都需要移动的电荷。金属中含有可以在原子之间自由移动的电子。当电池接入一个闭合电路时，它使这些电子沿一个方向漂移。这种电荷的定向流动称为电流。每秒钟通过某一点的电荷越多，电流就越大。
I = Q ÷ t
Here I is current in amperes (A), Q is charge in coulombs (C), and t is time in seconds (s). This equation tells us that current is the rate of flow of charge.
其中 I 是电流，单位为安培（A）；Q 是电荷，单位为库仑（C）；t 是时间，单位为秒（s）。这个公式告诉我们，电流就是电荷流动的速率。
2. Measuring Current | 测量电流
u need to measure a very small current, you may use milliamperes. Remember: 1 A = 1000 mA.
电流以安培为单位，常简称为安（A），电流的符号是 I。测量电流的仪器是电流表。它必须串联在电路中，也就是与电路其余部分处于同一个回路中。如果需要测量很小的电流，可以使用毫安。记住：1 A = 1000 mA。
In a circuit diagram, an ammeter is drawn as a circle with the letter A inside. It has very low resistance so it does not reduce the current significantly. When you connect an ammeter, you should always start with the largest range and then move to a smaller range if needed.
在电路图中，电流表画成一个圆圈，里面写着字母 A。它的电阻很小，因此不会明显减小电路中的电流。连接电流表时，应始终先使用大量程，如有需要再调到小量程。
3. Voltage as Push | 电压作为推动力
Voltage is the measure of energy given to each unit of charge. It is also called potential difference (p.d.). A battery does work on charges, giving them electrical energy. The bigger the voltage, the more energy each coulomb of charge carries. For example, a 9 V battery gives 9 joules of energy to every coulomb of charge that passes through it.
电压是每单位电荷所获得能量的量度，也称为电势差。电池对电荷做功，给它们电能。电压越大，每库仑电荷携带的能量就越多。例如，9 V 电池给通过它的每库仑电荷提供 9 焦耳的能量。
V = E ÷ Q
In this formula, V is voltage in volts (V), E is energy in joules (J), and Q is charge in coulombs (C). One volt means one joule of energy is transferred for every coulomb of charge that passes.
在这个公式中，V 是电压，单位为伏特（V）；E 是能量，单位为焦耳（J）；Q 是电荷，单位为库仑（C）。1 伏特表示每通过 1 库仑电荷就转移 1 焦耳的能量。
4. Measuring Voltage | 测量电压
Voltage is measured in volts (V). The symbol for voltage is V. A voltmeter is connected in parallel across the component being tested. This means the voltmeter provides an alternative path, but it has very high resistance, so almost no current flows through it. This allows the voltmeter to measure the energy difference without changing the circuit current.
电压以伏特（V）为单位，电压的符号是 V。电压表与被测元件并联。这意味着电压表提供了一条替代路径，但它的电阻非常大，所以几乎没有电流通过它。这样电压表就能测量能量差，而不会改变电路中的电流。
A typical AA cell provides about 1.5 V, while a car battery provides about 12 V. In a circuit diagram, a voltmeter is drawn as a circle with the letter V inside. Always connect the voltmeter across the two points you want to compare.
一节普通的 AA 电池提供约 1.5 V 的电压，汽车电池提供约 12 V 的电压。在电路图中，电压表画成一个圆圈，里面写着字母 V。测量时一定要把电压表连接在你想比较的两个点之间。
5. Series Circuits: Current | 串联电路中的电流
n series. If you add more bulbs in series, the total resistance increases and the current becomes smaller.
在串联电路中，元件一个接一个地连接在同一个回路里。电路中没有可供电流分流的节点。因此，回路中每一点的电流相同。关键规律是：串联时 I₁ = I₂ = I₃。如果串联更多灯泡，总电阻增大，电流会变小。
I(series) = I₁ = I₂ = I₃
This means if you place several ammeters around a series circuit, they will all read the same value. The current is not used up by the components, even though energy is transferred.
这意味着如果你在串联电路的不同位置放置多个电流表，它们的读数都相同。即使元件转移了能量，电流也不会被“用掉”。
6. Series Circuits: Voltage | 串联电路中的电压
The voltage across the battery or power supply is shared between the components in a series circuit. The sum of the individual voltages across the components equals the total supply voltage. For identical bulbs, the voltage is shared equally. For different bulbs, the bulb with the larger resistance gets a larger share of the voltage.
串联电路中，电池或电源电压会在各元件之间分配。各元件两端电压之和等于电源总电压。对于相同的灯泡，电压平均分配。对于不同的灯泡，电阻较大的灯泡分得的电压较多。
V(supply) = V₁ + V₂ + V₃
For example, two identical bulbs in series across a 6 V battery will each have 3 V. If one bulb has twice the resistance of the other, it will receive twice the voltage: 4 V and 2 V.
例如，两个相同灯泡串联接在 6 V 电池上，每个灯泡分得 3 V。如果一个灯泡的电阻是另一个的两倍，它分得的电压也会是另一个的两倍：分别为 4 V 和 2 V。
7. Parallel Circuits: Current | 并联电路中的电流
In a parallel circuit, the components are connected on separate branches, so there are junctions. The current from the battery splits at a junction. The total current leaving the battery is equal to the sum of the currents in all the branches. If the branches have equal resistance, the current splits equally. If not, the branch with lower resistance carries more current.
在并联电路中，各元件连接在独立的支路上，因此存在节点。电池输出的电流在节点处分开。电池流出的总电流等于各支路电流之和。如果各支路电阻相同，电流平均分流；如果不同，电阻较小的支路电流较大。
I(total) = I₁ + I₂ + I₃
This rule is useful when predicting readings on ammeters placed near the battery and in each branch. The ammeter near the battery records the largest current because it measures the total current before it splits.
这一规律在预测电池附近和各支路中电流表的读数时很有用。靠近电池的电流表读数最大，因为它测量的是电流分开前的总电流。
8. Parallel Circuits: Voltage | 并联电路中的电压
In a parallel circuit, every branch is connected directly across the battery. This means each branch receives the full battery voltage. For example, two bulbs in parallel across a 6 V battery each receive 6 V. That is why parallel circuits are used in homes: all appliances work at the same voltage.
在并联电路中，每条支路都直接
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