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Newton's Law of Cooling

The law states that the rate of loss of heat from a body is directly proportional to the mean difference of temperature between the body and the surroundings provided the excess temperature is small.


Suppose a body emits ΔQ energy in Δt second and the mean temperature of the body during this interval is θ and that of the surroundings is θ, where , θ1 is the temperature of the hot body at the beginning of the interval and θ2 at the end of the interval. Then,

where K is a constant which depends on the area and nature of the exposed surface.

Newton's law of cooling can be applied to the cooling of a cup of coffee on the table, to the case of the loss of heat through the walls of a room etc.

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