IIT JEE Physics (1978-2018: 41 Years) Topic-wise Complete Solutions

# Pressure in Two Connected Bottles

## Objective

To clarify the concept of pressure in an interesting manner.

## Procedure

Make holes near the bottom of two bottles and connect them with a transparent pipe. Fill colored water in bottle 1 upto the 3/4 level and keep the bottle 2 empty. Close the cap of two bottles. Open the cap of bottle 2. Let atmospheric pressure be $$p_0$$. Ask the following questions:

1. Pressure of air in bottle 1 is (i) less than $$p_0$$ (ii) more than $$p_0$$ (iii) equal to $$p_0$$?
2. Pressure of air in bottle 2 is (i) less than $$p_0$$ (ii) more than $$p_0$$ (iii) equal to $$p_0$$?
3. If the cap of the bottle 1 is opened, what kind of water flow do you expect?
• No water will flow
• Some water will flow from bottle 1 to bottle 2
• Water will be equally divided in both bottles

## Discussion

The solution is:

1. Bottle 1 is open. So pressure in it is $$p_0$$. At the tube level pressure in bottle is also the same. As you go up in bottle 1 pressure decreases by $$h\rho g$$. So pressure of air in bottle 1 is less than $$p_0$$.
2. $$p_0$$ as it is open to atmosphere.
3. Water will be equally divided in the two bottles.