The coefficient of linear expansion of a crystal in one direction is  and that in every direction perpendicular to it is .  The coefficient of cubical expansion is :

For O₂ gas

A steel sphere is to be passed through a circular brass ring.  At 20^o C the outer diameter of sphere is 25 cm and the inner diameter of the ring is 24.9 cm if both are heated together, then temperature at which the sphere will just pass through the ring will be :
(Take coefficient of linear expansion of steel= and that of brass = )