Question

Prove that beta is equals to 2 alpha

Answer 1

Answer:

α : the coefficient of linear expansion

β : the coefficient of surface expansion

Then a length increases as

L → L ( 1 + α ΔT)

But this means that for isotropic (same in every direction) expansion a surface (length x length) increases as

A → A ( 1 + α ΔT)( 1 + α ΔT) ≈ A (1 +2 α ΔT)

where we have neglected the (usually very small) square term (α ΔT)² .

Comparing with the (definition of β) expression

A → ( 1 + βΔT) , we see the relation

β = 2α .