Why does a sample containing compounds with chiral carbons have no effect on plane polarised light?

For a sample containing chiral carbons to have no effect on plane polarised light there must be an equal amount of each enantiomer in the sample. Enantiomers rotate plane polarised light by the same amount but in different directions - therefore if there is the same amount of each enantiomer in the sample (a racemate/ racemic mixture) the net rotation will be 0 as they will cancel eachother out. A racemate is produced due to the planar carbonyl structure being susceptible to nucleophillic attack from both above and below- this creates an equal amount of each enantiomer.