章节大纲

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  • 电力和电力能源使用

    A girl uses a hair dryer to dry her long hair quickly.

    Miranda has to use a hair dryer in order to dry her long hair quickly enough to get to school on time. She has a powerful hair dryer that dries her hair faster than a less powerful hair dryer would. That’s because a more powerful hair dryer changes electric current to more quickly.
    ::米兰达必须用一个吹毛机来快速地擦干她的长发,以便及时赶到学校。 她有一个强大的吹毛机,比一个不那么强大的吹毛机干得更快。 这是因为一个更强大的吹毛机能将电流改变得更快。

    Electric Power
    ::电力发电

    The rate at which a device changes electric current to another form of is called electric power . The SI unit for power—including electric power—is the watt . A watt equals 1 joule of energy per second. High wattages are often expressed in kilowatts, where 1 kilowatt equals 1000 watts. The power of an electric device, such as a hair dryer, can be calculated if you know the voltage of the and how much current the device receives. The following equation is used:
    ::设备将电流转换为另一种电流的速率称为电动。 SI的电源单位—— 包括电力—— 是瓦特。 一瓦特等于每秒1焦耳的能量。 高瓦往往以千瓦特表示, 1千瓦特等于1000瓦特。 电机的功率, 如吹毛机等, 如果知道电机的电压和电流, 可以计算出电机的功率。 使用以下方程式:

    Power (watts) = Current (amps) × Voltage (volts)

    Assume that Miranda’s hair dryer is the only electric device in a 120-volt circuit that carries 15 amps of current. Then the power of her hair dryer in kilowatts is:
    ::假设米兰达的吹风机是120伏电路中唯一一个携带15安培电流的电动装置。 那么她的吹风机在千瓦中的功率是:

    Power = 15 amps × 120 volts = 1800 watts, or 1.8 kilowatts

    Q: If a different hair dryer is plugged into a 120-volt circuit that carries 10 amps of current. What is the power of the other hair dryer?
    ::问题:如果一个不同的吹毛机被插入一个带有10安培电流的120伏电路。另一个吹毛机的功率是什么?

    A: Substitute these values in the power equation:
    ::A: 以这些数值替代功率方程:

    Power = 10 amps × 120 volts = 1200 watts, or 1.2 kilowatts

    Electrical Energy Use
    ::电气能源使用

    Did you ever wonder how much electrical energy it takes to use an appliance such as a hair dryer? Electrical depends on the power of the appliance and how long it is used. It can be calculated with this equation:
    ::你有没有想过使用吹毛机这样的电器需要多少电能?电力取决于电器的功率和使用时间。可以用这个方程式来计算:

    Electrical Energy = Power × Time

    If Miranda uses her 1.8-kilowatt hair dryer for 0.2 hours, how much electrical energy does she use?
    ::如果米兰达用她1.8千瓦的吹毛机做0.2小时 她能用多少电能?

    Electrical Energy = 1.8 kilowatts × 0.2 hours = 0.36 kilowatt-hours

    Electrical energy use is typically expressed in kilowatt-hours, as in this example. How much energy is this? One kilowatt-hour equals 3.6 million joules of energy.
    ::电能使用通常以千瓦时表示,例如,这个例子。这需要多少能源?一千瓦小时等于360万焦耳的能源。

    Q: Suppose Miranda were to use a 1.2-kilowatt hair dryer for 0.2 hours. How much electrical energy would she use then?
    ::问:假设米兰达在0.2小时使用1.2千瓦的吹毛机。她将使用多少电能?

    A: She would use:
    ::A:她将使用:

    Electrical Energy = 1.2 kilowatts × 0.2 hour = 0.24 kilowatt-hours

    Take a trip to the National Grid in the video below: 
    ::前往国家网格旅游, 影片如下:

    Summary
    ::摘要

    • Electric power is the rate at which a device changes electric current to another form of energy. The SI unit of power is the watt. Electric power can be calculated as current times voltage.
      ::电能是设备将电流改变为另一种能源的速率。 SI的功率单位是瓦特。 电能可以计算为当值乘以电压。
    • Electrical energy use equals the power of the appliance multiplied by the amount of time the appliance is used.
      ::电能使用等于用具的功率乘以用具使用时间。

    Review
    ::回顾

    1. Define electric power. What is the SI unit for power?
      ::电源的定义。
    2. A microwave is the only electric device in a 120-volt circuit. If the circuit has 7.5 amps of current, what is the electric power of the microwave?
      ::微波是120伏电路中唯一的电力装置,如果电路有7.5安普的电流,微波的电能是什么?
    3. Calculate the electrical energy use of the microwave in question 2 if it used for 0.05 hours.
      ::计算问题2中微波的电能用量,如果微波用在0.05小时。