Question

Assertion
An open tube manometer is a useful instrument for measuring pressure differences.
Reason
\[1\,{\text{bar}} = {\text{1}}{{\text{0}}^5}\,{\text{Pa}}\]
A. Both assertion and reason are correct and reason is the correct explanation for the assertion
B. Both assertion and reason are correct and reason is the correct explanation for the assertion
C. Assertion is correct but reason is incorrect
D. Both assertion and reason are incorrect

Answer 1

Hint: Explain why the open tube manometer is a useful instrument for measuring pressure differences. Check whether the given reason satisfactorily explains why open tube manometer is good for measuring pressure differences.

Complete step by step answer:
An open tube manometer is the simplest pressure gauge.An open tube manometer has a container in which the gas whose pressure is to be measured is filled and a U-shaped tube containing a liquid (mercury). One end of the U-shaped tube is free to air and the other end is connected to the container in which gas whose pressure is to be determined is filled. The pressure difference of the gas in the container is indicated by the height of mercury level on the tube. Hence, by this method the pressure difference can be measured very easily.
Therefore, the open tube manometer is a useful instrument for measuring the pressure differences. Hence, the assertion is correct.Bar and Pascal both are the units of pressure. The conversion factor between the units bar and Pascal is \[{\text{1}}{{\text{0}}^5}\]. Hence, one bar is equal to \[{\text{1}}{{\text{0}}^5}\,{\text{Pa}}\].
Therefore, \[1\,{\text{bar}} = {\text{1}}{{\text{0}}^5}\,{\text{Pa}}\] is correct.Hence, the reason is also correct.
The reason \[1\,{\text{bar}} = {\text{1}}{{\text{0}}^5}\,{\text{Pa}}\] does not explain why the open tube manometer is a useful instrument for measuring the pressure differences.
Hence, the assertion and reason both are correct but the given reason is not the correct explanation for the given assertion.
Hence, the correct option is B.

Note:One can also explain the answer of the given question in a reverse way. One can check whether the given assertion gives the correct relation with the given reason.