alcohol test by k2cr2o7 how colour chnage from orange to green

Alcohols react with oxidising agent like potassium dichromate,K₂Cr₂O₇ in dil.H2SO4.However the differnt alcohols react differently during this reaction.
When alcohol treated with acidified K₂Cr₂O_7,if reacton occurs, orange colour solution containing dichromate ions get reduced to green solution containing chromium ions.The electron half equation for this reaction can be given as-
Cr₂O₇^2- + 14H⁺ + 6e^- ---------------> 2Cr³⁺ + 7H₂O
Primary and secondary alcohols give this test but tertiary not.So colour of acidified potassium dichromate gets changes from orange to green.Primary alcohols oxidised to first aldehyde and then to acids.But secondary alcohols oxidised to ketone which further not oxidised.