Coefficients of linear expansion of an isotropic solid along three rectangular axes in the solid are ${\mathrm{\alpha }}_{\mathrm{x},}{\mathrm{\alpha }}_{\mathrm{y}} \mathrm{and} {\mathrm{\alpha }}_{\mathrm{z}.}$ Coefficient of cubical expansion of the solid for small change in temperature can be expressed as : ( assume ${\mathrm{\alpha }}_{\mathrm{x}},{\mathrm{\alpha }}_{\mathrm{y}} \mathrm{and} {\mathrm{\alpha }}_{\mathrm{z}}$to be small quantities)

• A

  ${\mathrm{\alpha }}_{\mathrm{x}}+{\mathrm{\alpha }}_{\mathrm{y}}+{\mathrm{\alpha }}_{\mathrm{z}}$

• B

  ${\mathrm{\alpha }}_{\mathrm{x}} {\mathrm{\alpha }}_{\mathrm{y} }{\mathrm{\alpha }}_{\mathrm{z}}$

• C

  $\sqrt{{\mathrm{\alpha }}_{\mathrm{x}}^2+{\mathrm{\alpha }}_{\mathrm{y}}^2+{\mathrm{\alpha }}_{\mathrm{z}}^2}$

• D

  none of these