Question

Which of the following statements is/are correct?
(i) A simple U-tube manometer can measure negative gauge pressures.
(ii) Both ends of a U-tube manometer are exposed to the atmosphere. There exists a possibility that the height difference in the manometer is non-zero.

• A. Only (i) is correct
• B. Only (ii) is correct
• C. Both (i) and (ii) are correct
• D. None of these are correct

Answer 1

The correct option is C Both (i) and (ii) are correct

The height of the manometric fluid in a U-tube manometer in the test column would fall if there is a positive gauge pressure. The height would increase if there is a negative gauge pressure. Thus, it is possible to measure negative gauge pressures with a U-tube manometer. However, the negative pressure cannot fall below $-1\text{Bar}$.

The height difference may be non-zero when there are multiple immiscible fluids used in the same manometer. Even though the pressure is same on both surfaces, the height would be different as the fluid with higher density will be at a lower height.
Thus, both statements are correct.