Q.

The value of coefficient of volume expansion of glycerin is 5×10-4K-1. The fractional change in the density of glycerin for a rise of 40°C in its temperature, is    [2015]
 

1 0.025  
2 0.010  
3 0.015  
4 0.020  

Ans.

(4)

Let ρ0 and ρT be densities of glycerin at 0°C and T°C respectively. Then,

        ρT=ρ0(1-γΔT)

where γ is the coefficient of volume expansion of glycerine and ΔT is rise in temperature.

        ρTρ0=1-γΔT  or  γΔT=1-ρTρ0

Thus,  ρ0-ρTρ0=γΔT

Here, γ=5×10-4K-1 and ΔT=40°C=40K

   The fractional change in the density of glycerin

=ρ0-ρTρ0=γΔT=(5×10-4K-1)(40K)=0.020