This is given by the fact that by an equation omega square equal to g k, what does it mean? Remember omega is actually period, see omega is basically 2 pi by T square and K is 2 pi by lambda. What it means is that k is related to length, omega is related to frequency and period. What this relation tells is very interesting. It says that for a given wave length, there can only be a given period because omega and K are related to each other not independent to each other, not independent to each other. That means if you have omega means T, let us say I have a wave of 10 second period. Then the 10 second period wave will have only so much of length. It cannot have like a 10 second period of wave cannot have length of 100 meter or also 200 meter also 300 meter it cannot have.