Specifications

Ver SG 9/200 9 Sharp Electronics Corporation
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Microwave Power: Its Measurement and Its Meaning
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To properly develop a sense of timing in microwave cooking, it is first necessary to know
how much power is available in the oven. A microwave oven is not like a conventional
hot oven. There is no excess of heat available. All of the microwave energy is absorbed
by the food. There is little or no wasted energy.
We measure power by converting the microwave energy into heat and measuring it in a
simple calorimeter. The tools we need are a Pyrex measuring cup, a thermometer, a
clock and some cold water.
Pour two cups of cold tap water in
the Pyrex measuring cup. Note the
temperature. Heat the water in the
microwave oven for one minute and
measure the temperature again. The
difference in temperature times 17.5
is the power in watts. This is the
amount of power generated in the
oven in one hour. One-sixtieth
(1/60
th
) of this power is available
every minute.
If the oven power is 1000 watts (1
kilowatt), then there are 3413 British
Thermal Units of heat available with
which to cook.
A British Thermal Unit (Btu) is the amount of heat which will raise the temperature of
one pound of water one degree Fahrenheit. In terms of BTU then, a one kilowatt oven
puts out 57 Btu each minute, and if one pound of water were placed in the oven it should
increase in temperature 57°F. in one minute.
With this information the effect of food composition on heating time can be discussed
somewhat more intelligently. Most foods contain moisture in varying amounts with the
exception of pure fats like salad oils, shortening and lard. Another exception is
dehydrated foods which do not depend on moisture to convert microwave energy into
heat. The amount of moisture in a food has a direct bearing on its heating rate in a
microwave oven.