Calculate the coefficient of performance of a refrigerator working between  ${\text{-10}}^{\text{o}}\text{C}$ to  ${\text{20}}^{\text{o}}\text{C}$ is

$$\begin{gathered} {\text{temperature of source is T}}_{\text{1}}\text{=20+273=293\hspace{0.17em}K (converting into kelvin scale)} \\ \mathrm{temperature} \mathrm{of} \mathrm{sink} \mathrm{is} {\text{T}}_{\text{2}}\text{=-10+273=263\hspace{0.17em}K} \end{gathered}$$

For Refrigerator

$\begin{array}{rcl} & & \text{coefficient of performance is β=}\frac{{\text{T}}_{\text{2}}}{{\text{T}}_{\text{1}}{\text{-T}}_{\text{2}}}\\ & & \mathrm{substitute} \mathrm{the} \mathrm{given} \mathrm{values}\\ \mathrm{\beta }& =& \frac{263}{293-263}=\frac{263}{30}\\ & & \text{β=8.77}\end{array}$