Question 8
In a siphon, why does water flow from tank A at the higher level into tank B below it?
The right answer is the one marked above.
Because the pressure at the tube end in A exceeds the pressure at the end in B. At A the pressure is the pressure of the liquid column in the tank plus atmospheric pressure, while at B, open to the atmosphere, it is atmospheric pressure alone.
The size of the tank and the temperature of the water make no difference. Filling the tube at the start is needed to get the flow going, not to create the pressure difference.