A certain microwave oven produces microwaves of frequency 2450 MHzwith a power o

Question

A certain microwave oven produces microwaves of frequency 2450 MHzwith a power of 500 W. How long should it take to heat 519 g of water, initially at room temperature, to theboiling point? Assume that all the microwave energy is absorbed bythe water. (The microwave frequency is significant because thewater molecule has a rotational resonant frequency at 2450 MHz.This means that water very effectively absorbs radiant energy atthis frequency, thereby raising its rotational kinetic energy andits temperature. The specific heat of water is 4186J/kg–C°, and assume that the room temperature is20°C.)

Explanation / Answer

   Heat energy required bywater      H   =   m* c * T    mass ofwater   m   =   519   g    specific heat ofwater   c   =   4.2   J/g-0C    change intemperature   T   =   (100- 20)                                                    =   80   0C    H   =   519 *4.2 * 80          =   1.744* 105   J    Also   energy   =   power* time    timetaken      t   =   H/ P                                  =   1.744* 105 / 500                                  =   348.8   s

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