Newton’s law of cooling
When a hot body is placed in a room it emits heat energy
because of the combined effect of convection as well as radiation. The amount
of the heat energy that it can emit per one second can be calculated using this
law.
According to this law the rate of loss of heat energy is
directly proportional to temperature difference between the body and the
surroundings.
It simply means that when the difference between the body
temperature the surroundings temperature is more, the loss of heat energy will
be quick and vice versa.
It can be also proved that the rate of loss of heat energy is
equal to the rate of change of temperature.
We can also state the law as the rate of loss of temperature
is directly proportional to the temperature difference between the body and the
surroundings.
This law is valid only when the temperature difference
between the body and surrounding is small.
Problem and solution
A body at temperature
of hundred degrees centigrade is brought in the room of temperature 20°C. To
cool from hundred degrees centigrade and 80°C has taken a time of 10 minutes.
How much further time it will take to cool from 80°C to 60°C?
We have to solve this problem basing on the Newton law
cooling.
The rate of loss of heat energy or the rate of loss of
temperature is directly proportional to temperature difference between the body
and surroundings. By applying this rule to the two different cases available we
can solve the problem as shown.
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