Physics XI Notes for Physics Notes

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Water Equivalent Of A Substance

It is defined as the mass of water that will absorb or lose as same quantity of heat as the substance for the same change in temperature.
Let us consider a body having mass m, specific heat capacity s and change in temperature ∆θ.

Q = ms∆θ è1

If W be the water equivalent of the substance then,
Q = Wsw∆θ è2

Equating equation 1 and 2
ms∆θ = Wsw∆θ
W = ms/sw

In CGS system sw = 1calg-1K-1 then,
W = ms

Note: the water equivalent of a substance is numerically equal to the heat capacity of a substance in CGS system but not dimensionally.

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