Page 106 - Physics - XI

Q3. State the conditions which are necessary for Boyle's law to be valid.
Ans. (i) Temperature should remain constant. (ii) The quantity of the gas should remain constant.
(iii) The gas should behave as an ideal gas.

Q4. How does the presence of moisture in the closed tube aff ect the result?
Ans. The moisture will exert its own pressure on the mercury column.

Q5. What type of graph do you expect between P and V of a given mass of a gas?
Ans. A rectangular parabola

Q6. What is the use of mercury in Boyle's law apparatus?
Ans. Pressure diff erence is the diff erence of mercury levels in tube A and tube B. This diff erence added
algebraically to atmospheric pressure gives the pressure of air in tube A in cm of mercury.
Q7. Why is it necessary to make Boyle's law apparatus vertical?

Ans. If it is not vertical, the reading of mercury column will not be accurate.
Q8. Give the dependency of the pressure on the radius of tube AB and CD?

Ans. Pressure does not depend upon the radius (Area of cross-section) of tube.

Q9. What type of graph do you expect between P and 1/V?
Ans. A straight line

Q10. The apparatus when not in use should be kept covered to avoid the contamination of mercury
in the open tube. How will the oxidation of mercury aff ect the experiment? (NCERT)
Ans. When the apparatus is not in use, then it should be kept covered because pressure is measured in
terms of height of mercury column and the contamination of mercury will change its density and in
turn the value of pressure.

Q11. If the diameter of tube AB is large, then why would the estimation of curved portion be
unreliable? (NCERT)
Ans. If the diameter of the tube becomes large, then it will lead to the increase in the volume of curved
portion. It means that the error in its volume will get increased which ultimately leads to the error in
the length.

Q12. Why should the upper meniscus of the mercury in the two tubes recorded carefully using a
set-square? (NCERT)
Ans. While measuring the upper meniscus of the mercury in the two tubes, the set-square is usually
placed tangentially to the upper meniscus of mercury in order to determine its level (without any

error).

Q13. Comment on the two methods used for the estimation of volume of the curved portion of the
closed tube. What are the assumptions to be made for the two methods?
Ans. Both the methods used in the experiment were to analyse the variation of volume with pressure. First
method includes the volume of trapped air and second one includes the measurement of volume of
air for a given pressure.

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