电功 (W) 是电流所做的功，表示电能转化为其他形式能量的多少。
公式：\(W = UIt\)（电压×电流×时间）
推导：\(W = UIt = I^2Rt = \frac{U^2}{R}t\)
单位：焦耳 (J)，常用单位：千瓦时 (kW·h)，即"度"。
\(1\,\text{kW·h} = 3.6\times 10^6\,\text{J}\)
电能表（电度表）用来测量电路中消耗的电能。
Electric work (W) is the work done by current, representing energy converted from electrical to other forms.
Formula: \(W = UIt\) (voltage × current × time)
Derived: \(W = UIt = I^2Rt = \frac{U^2}{R}t\)
Unit: joule (J), common unit: kilowatt-hour (kW·h) ("degree").
\(1\,\text{kW·h} = 3.6\times 10^6\,\text{J}\)
An electric meter measures consumed electrical energy.
电功率 (P) 表示电流做功的快慢，即单位时间内电流所做的功。
定义式：\(P = \frac{W}{t}\)
计算公式：\(P = UI\)（最常用！）
推导式：\(P = I^2R = \frac{U^2}{R}\)（仅适用于纯电阻电路）
单位：瓦特 (W)，常用：千瓦 (kW)、毫瓦 (mW)
额定功率：用电器在额定电压下正常工作时的功率。
实际功率：用电器在实际电压下工作时的功率。
Electric power (P) represents the rate of doing electrical work — work done per unit time.
Definition: \(P = \frac{W}{t}\)
Formula: \(P = UI\) (most commonly used!)
Derived: \(P = I^2R = \frac{U^2}{R}\) (pure resistive circuits only)
Unit: watt (W), common: kilowatt (kW), milliwatt (mW)
Rated power: Power at rated (nominal) voltage.
Actual power: Power at actual operating voltage.
焦耳定律：电流通过导体产生的热量与电流的平方成正比，与导体的电阻成正比，与通电时间成正比。
公式：\(Q = I^2Rt\)
如果电路中只有纯电阻（电热器、灯泡等），则 \(Q = W = UIt = I^2Rt\)。
如果有电动机等非纯电阻元件，则 \(W > Q\)（电能部分转化为机械能）。
Joule's Law: Heat produced by current in a conductor is proportional to the square of current, to the resistance, and to the time of current flow.
Formula: \(Q = I^2Rt\)
For pure resistive circuits: \(Q = W = UIt = I^2Rt\).
With motors (non-pure-resistive): \(W > Q\) (some energy becomes mechanical work).
由 \(P = UI\) 和 \(I = \frac{U}{R}\)，可以推导出：
\(P = I^2R = \frac{U^2}{R}\)
串联电路中电流相同 → 功率与电阻成正比：\(P_1:P_2 = R_1:R_2\)
并联电路中电压相同 → 功率与电阻成反比：\(P_1:P_2 = \frac{1}{R_1}:\frac{1}{R_2} = R_2:R_1\)
From \(P = UI\) and \(I = \frac{U}{R}\):
\(P = I^2R = \frac{U^2}{R}\)
Series: same current → \(P_1:P_2 = R_1:R_2\)
Parallel: same voltage → \(P_1:P_2 = \frac{1}{R_1}:\frac{1}{R_2} = R_2:R_1\)
• LED灯泡: 5-20 W
• 日光灯: 20-40 W
• 电视机: 100-300 W
• 电冰箱: 100-200 W
• 空调: 1000-3000 W
• 电热水器: 1500-3000 W
• 微波炉: 800-1500 W
• LED bulb: 5-20 W
• Fluorescent lamp: 20-40 W
• TV: 100-300 W
• Fridge: 100-200 W
• A/C: 1000-3000 W
• Water heater: 1500-3000 W
• Microwave: 800-1500 W
调节电压，观察灯泡亮度变化和功率计算。灯泡额定电压 6V，额定功率 3W（电阻=12Ω）。低于额定电压时灯泡较暗，功率小于额定功率。
Adjust voltage to observe brightness and power. Bulb specs: 6V 3W (R=12Ω). Below rated voltage, the bulb is dimmer with less than rated power.
输入电器功率和使用时间，计算耗电量和电费。（按 0.6 元/kW·h 计算）
Enter appliance power and usage time to calculate energy consumption and cost. (Based on 0.6 yuan/kW·h)