欧姆定律计算器 — 电压、电流、电阻 & 功率

欧姆定律（V = I × R）关联任意电路中的电压、电流和电阻。输入任意两个已知值，本计算器即时求解第三个——并使用 P = V × I 计算消耗的功率（瓦特）。

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Frequently Asked Questions

什么是欧姆定律？

欧姆定律指出：导体两端的电压（V）等于通过它的电流（I）乘以其电阻（R）：V = I × R。这是电子和电气工程中最基本的定律之一。单位：电压伏特（V）、电流安培（A）、电阻欧姆（Ω）。

欧姆定律的三个公式是什么？

V = I × R（计算电压）；I = V / R（计算电流）；R = V / I（计算电阻）。功率相关：P = V × I = I² × R = V² / R，其中P为功率（瓦特）。记忆技巧：将VIR写成三角形，用手遮住要求的量，剩余两量即为计算关系。

如何计算电路中的功率？

功率 P = V × I。结合欧姆定律：P = I² × R（已知电流和电阻）；P = V² / R（已知电压和电阻）。例如：120V家用插座，10Ω电热丝：I = 120/10 = 12A；P = 120 × 12 = 1440W = 1.44kW。

串联和并联电路有何不同？

串联电路：电流相同，电压分担，总电阻 = R1+R2+...；总电压 = V1+V2+...。并联电路：电压相同，电流分担，总电阻 = 1/(1/R1+1/R2+...)，总电阻小于最小单个电阻。家庭用电是并联电路（各电器独立工作，断一个不影响其他）。

欧姆定律适用于所有材料吗？

欧姆定律适用于"欧姆材料"（如铜、铝等金属导体），在温度恒定时V-I关系为线性。不适用于非欧姆元件：二极管（只允许单向电流）、晶体管（受控电流源）、灯泡（温度升高电阻增大）、电容器和电感（交流下有频率相关的阻抗）。

家庭电路用电安全与欧姆定律有何关系？

保险丝和断路器利用欧姆定律保护电路：过载时电流I = V/R过大，超过保险丝额定值时断路。举例：家用220V，一台2200W空调电流 = 2200/220 = 10A，一台1000W热水器电流 = 1000/220 ≈ 4.5A，两台合计14.5A，接近普通16A断路器额定值。

LED灯为什么需要限流电阻？

LED不是欧姆元件，正向导通后电阻很小，电流会急剧上升导致烧毁。需用串联限流电阻控制电流。计算：R = (电源电压 - LED正向电压) / 目标电流。例如5V电源驱动3V/20mA LED：R = (5-3)/0.02 = 100Ω。应选择稍大（如120Ω）以留安全余量。

欧姆定律在实际排障中如何应用？

万用表 + 欧姆定律可诊断大多数电路故障：测电压找断路（断路处电压异常）；测电阻找短路（短路处电阻接近零）；测电流找过载（电流超额定值）。例如：灯不亮，测灯两端电压为0（应为220V），说明断路在灯之前。测得灯丝电阻无穷大，说明灯丝断了。

Ohm's Law Formula

Ohm's Law states that the voltage across a conductor is directly proportional to the current through it, with resistance as the constant of proportionality. The three fundamental forms of the formula are:

Voltage (V)

V = I × R

Example: 2 A through 6 Ω → 2 × 6 = 12 V

Current (I)

I = V / R

Example: 9 V across 450 Ω → 9 / 450 = 0.02 A (20 mA)

Resistance (R)

R = V / I

Example: 12 V with 2 A → 12 / 2 = 6 Ω

Power Formula

Power (measured in watts) describes how much energy a circuit consumes per second. It can be derived from any two of the three Ohm's Law variables:

P = V × I

Example: 12 V × 2 A = 24 W

P = I² × R

Example: (2 A)² × 6 Ω = 24 W

P = V² / R

Example: (12 V)² / 6 Ω = 24 W

How to Use This Calculator

  1. Select what you want to solve for — choose Voltage, Current, or Resistance using the mode buttons at the top.
  2. Enter the two known values— fill in the two input fields. Units are shown next to each field (V, A, or Ω).
  3. Read the result instantly — the calculator shows all four values: Voltage, Current, Resistance, and Power.
  4. Copy the result — click the Copy button to copy all four values to your clipboard.

Common Applications

LED Circuits

Use Ohm's Law to calculate the current-limiting resistor for an LED. For a 5 V supply, an LED forward voltage of 2 V, and desired current of 20 mA: R = (5 V − 2 V) / 0.02 A = 150 Ω.

Motor Control

Determine the stall current or running current of a DC motor. Knowing the motor's winding resistance and supply voltage, you can calculate the maximum current draw and size your fuse accordingly.

Heating Elements

Calculate the power output of a resistive heating element. A 10 Ω element on a 120 V mains supply draws 12 A and dissipates 1440 W (1.44 kW) of heat.

Voltage Dividers

Design voltage dividers for sensor circuits and analog-to-digital converter inputs by applying Ohm's Law across each resistor in the chain.

Quick Reference Table

Common voltage and resistance combinations with calculated current and power:

Voltage (V)Resistance (Ω)Current (A)Power (W)
51000.050.25
94700.01910.172
1210000.0120.144
242200.1092.618
120602240
24010245760

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