# Plate Theory and Extensions - Column Efficiency > Page 54

(48)

The peak width
at the points of inflexion of the elution curve is* twice the standard
deviation* of the Poisson or Gaussian curve and thus, from equation (47),
the variance (the square of the standard deviation) will be equal to (n), the
total number of plates in the column.

The variance
of the band (s_{v}^{2}) in milliliters^{2} of mobile phase will be given by,

s^{2 }= n(v_{m }+ Kv_{s})^{2}

^{ }

Now,

Thus,

Thus, the variance of the peak is inversely proportional to the number of theoretical plates in the column. Thus, the greater (n), the narrower the peak, and the more efficiently has the column constrained peak dispersion.