Electric Power · 电功率
| English | 中文 | Pinyin · 拼音 |
|---|---|---|
| electric power/ɪˈlektrɪk ˈpaʊə/ | 电功率 | diàn gōng lǜ |
| watt/wɒt/ | 瓦特 | wǎ tè |
Why a heater glows and a wire stays cool
- A toaster's element glows red-hot, yet the cord feeding it barely warms.
- Both carry the same current — but the element dissipates far more energy per second.
- The rate at which a component turns electrical energy into heat or light is electric power 电功率.
- Getting the power formulas straight lets you size heaters, bulbs and fuses.
为什么加热器发光而导线保持凉爽
- 烤面包机的发热丝烧得通红,可给它供电的电线却几乎不热。
- 两者通过相同的电流——但发热丝每秒耗散的能量多得多。
- 一个元件把电能变成热或光的速率就是电功率。
- 弄清功率公式,你就能给加热器、灯泡和保险丝定规格。
Power in a circuit
- Electric power is the rate of energy transfer: $P = IV$ (current times voltage).
- Its unit is the watt 瓦特, as in mechanics ($1\ \text{W} = 1\ \tfrac{\text{J}}{\text{s}}$).
- Every second, a component converts $P$ joules of electrical energy into another form.
- For a resistor that "other form" is heat; for a bulb, heat and light.
电路中的功率
- 电功率是能量传递的速率:$P = IV$(电流乘以电压)。
- 它的单位是瓦特,和力学中一样($1\ \text{W} = 1\ \tfrac{\text{J}}{\text{s}}$)。
- 每一秒,一个元件把 $P$ 焦耳的电能变成另一种形式。
- 对电阻,那种"另一种形式"是热;对灯泡,是热和光。
Voltage, current and power · 电压、电流与功率
Change the voltage and resistance and watch the current and dissipated power respond. · 改变电压和电阻，观察电流和耗散功率的响应。
A bulb carries $0.5\ \text{A}$ at $12\ \text{V}$. What power does it dissipate, in watts? · 一个灯泡在$0.5\ \text{A}$时通过$12\ \text{V}$。它消耗的功率是多少瓦特？
$P = IV = 0.5 \times 12 = 6\ \text{W}$.
Electric power is measured in . · 电功率的计量单位是。
$1\ \text{W} = 1\ \tfrac{\text{J}}{\text{s}}$.
Three forms of the same law
- Combine $P = IV$ with Ohm's law $V = IR$ to get two more useful forms.
- $P = I^2 R$ — handy when you know the current and resistance.
- $P = \dfrac{V^2}{R}$ — handy when you know the voltage and resistance.
- All three give the same power; pick whichever fits your known quantities.
同一定律的三种形式
- 把 $P = IV$ 与欧姆定律 $V = IR$ 结合,得到两个更有用的形式。
- $P = I^2 R$——已知电流和电阻时方便。
- $P = \dfrac{V^2}{R}$——已知电压和电阻时方便。
- 三者给出相同的功率;选适合你已知量的那个。
A current of $2\ \text{A}$ flows through a $3\ \Omega$ resistor. What power is dissipated, in watts? · 电流$2\ \text{A}$流过$3\ \Omega$电阻器。消耗的功率是多少，单位为瓦特？
$P = I^2R = 2^2 \times 3 = 12\ \text{W}$.
You know a resistor's current and resistance. Which power formula is most direct? · 已知某电阻的电流和电阻值。哪个功率公式最直接？
$P = I^2R$ uses exactly the current and resistance you know. · $P = I^2R$直接使用你已知的电流和电阻值。
Select all · 所有 correct expressions for electric power. · 选择所有关于电功率的正确表达式。
The first three are equivalent power formulas. $I/V$ is not power. · 前三个是等效的功率公式。$I/V$不是功率。
Energy used over time
- Power is energy per second; total energy used is $E = Pt$.
- This is what electricity meters measure and what you pay for.
- A high-power device left on briefly can use less energy than a low-power one left on for hours.
- Fuses are rated by the current (and so the power) a wire can safely carry.
一段时间内所用的能量
- 功率是每秒的能量;所用总能量是 $E = Pt$。
- 这正是电表所测量、你所支付的东西。
- 高功率设备开一小会儿,可能比低功率设备开几个小时耗能更少。
- 保险丝按导线能安全承载的电流(以及功率)来定额。
A $6\ \text{W}$ bulb is left on for $10\ \text{s}$. How much energy does it use, in joules? · 一个$6\ \text{W}$灯泡打开了$10\ \text{s}$秒。它消耗了多少焦耳的能量？
$E = Pt = 6 \times 10 = 60\ \text{J}$.
Watch which power formula fits your data. $P = I^2R$ uses current and resistance; $P = V^2/R$ uses voltage and resistance. Plugging voltage into the $I^2R$ form (or current into $V^2/R$) is a common slip.
注意哪个功率公式适合你的数据。$P = I^2R$ 用电流和电阻;$P = V^2/R$ 用电压和电阻。把电压代入 $I^2R$ 形式(或把电流代入 $V^2/R$)是常见的失误。
A bulb carries $0.5\ \text{A}$ at $12\ \text{V}$. What power does it dissipate?
- $P = IV = 0.5 \times 12 = 6\ \text{W}$.
Left on for $10\ \text{s}$, it uses $E = Pt = 6 \times 10 = 60\ \text{J}$ of energy.
一个灯泡在 $12\ \text{V}$ 下通过 $0.5\ \text{A}$。它耗散多大功率?
- $P = IV = 0.5 \times 12 = 6\ \text{W}$。
开 $10\ \text{s}$,它用掉 $E = Pt = 6 \times 10 = 60\ \text{J}$ 的能量。
Electric power is the energy transferred per second: $P = IV = I^2R = \dfrac{V^2}{R}$ (in watts). A resistor turns it into heat. Total energy used is $E = Pt$ — what electricity meters measure. Pick the power form that matches your known quantities.
电功率是每秒传递的能量:$P = IV = I^2R = \dfrac{V^2}{R}$(单位瓦特)。电阻把它变成热。所用总能量是 $E = Pt$——电表所测量的东西。选与你已知量相符的功率形式。