We know that we get first resonance when the length of the air column is λ/4. We get second resonance when the length of the air column is 3λ/4. This is because we get a node at the surface of the water after λ/4 distance in the first case and 3λ/4 in the second case. My question is that what happens if we take the length of the air column not be λ/4 or 3λ/4 but somewhere in between say λ/2. How would the wave diagram look like? I am posting all the three cases' diagrams. Please verify if the last diagram (λ/2 case) would be like the one I have posted or not? I think not because we can never get an anti-node at an open end. So how would the wave diagram look like? Thank you, reply soon!