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Heather C fragte in Science & MathematicsPhysics · vor 1 Jahrzehnt

Help with a microwave problem?

A certain microwave oven produces microwaves of frequency 2450 MHz with a power of 500 W. How long should it take to heat 477 g of water, initially at room temperature, to the boiling point? Assume that all the microwave energy is absorbed by the water. (The microwave frequency is significant because the water molecule has a rotational resonant frequency at 2450 MHz. This means that water very effectively absorbs radiant energy at this frequency, thereby raising its rotational kinetic energy and its temperature. The specific heat of water is 4186 J/kg–C°, and assume that the room temperature is 20°C.)

2 Antworten

Relevanz
  • vor 1 Jahrzehnt
    Beste Antwort

    OK. Let's get rid of the waffle.

    How much heat energy is required to raise the temperature of 0.477 kg of water from 20C to 100C?

    If the heat energy is supplied at a rate of 500 J/s, how long will it take to supply that amount of energy?

    Time taken = T

    Energy required = mass * specific heat * change in temperature

    E = 0.477 * 4186 * (100 - 20) = 159738 J

    T = 159738 / 500 = 319.5 s

  • Steve
    Lv 7
    vor 1 Jahrzehnt

    Energy absorbed = Electrical energy in

    m*S*dT = W*t → t = mSdT/W = .477*4186*(100 - 20)/500

    t = 319.5 sec

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