# An inclined manometer is a useful device for measuring small pressure differences. The formula given in Section

## Question:

An inclined manometer is a useful device for measuring small pressure differences.

The formula given in Section 3.4 for the pressure difference in terms of the liquid-level difference h remains valid, but while h would be small and difficult to read for a small pressure drop if the manometer were vertical, L can be made quite large for the same pressure drop by making the angle of the inclination, θ, small.

(a) Derive a formula for h in terms of L and θ.

(b) Suppose the manometer fluid is water, the process fluid is a gas, the inclination of the manometer is θ = 15°, and a reading L = 8.7 cm is obtained. What is the pressure difference between points 1 and 2 ?

(c) The formula you derived in Part (a) would not work if the process fluid were a liquid instead of a gas. Give one definite reason and another possible reason.

Formula in section 3.4

P1 + ρ1gd1 = P2 + ρ2gd2 + ρfgh

P1 - P2 = (ρ- ρ)gh

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