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Grade 10Thermal Physics

(1)A uniform tube closed at one end, contains a pallet of mercury 10cm long. When the tube is kept vertically with the closed end upward, the length of the air column trapped is 20cm. Find the length of air column trapped when the tube is inverted so that the closed end goes down. Atmospheric pressure = 75cm of mercury.
(2)A glass tube sealed at both ends, is 100cm long. It lies horizontally with the middle 10cm containing mercury. The two ends of the tube contain air at 27degrees C and at a pressure 76cm of mercury. The air column on one side is maintained at 0 deg C and the other side is maintained at 127deg C. Calculate the length of air column on the cooler side. Neglect the changes in the volume of the mercury and of the glass.
(3)An ideal gas is trapped between a mercury column and the closed end of a narrow vertical tube of uniform base containing the column. The upper end of the tube is open 2 the atmosphere. The atmospheric pressure equals 76cm of mercury. The lengths of mercury column and the trapped air column are 20cm and 43cm respectively. What will be the length of the air column when the tube is tilted slowly in a vertical plane through an angle of 60degrees? assume the temperature 2 remain constant.

Profile image of Aditi Chauhan
12 Years agoGrade 10
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1 Answer

Profile image of Askiitians Tutor Team
ApprovedApproved Tutor Answer1 Year ago

Let's tackle these three problems step by step, focusing on the principles of gas laws and hydrostatics. Each scenario involves understanding how pressure and temperature affect the behavior of gases in different configurations.

1. Length of Air Column When the Tube is Inverted

In the first scenario, we have a uniform tube closed at one end containing a mercury column and an air column. Initially, the tube is vertical with the closed end up, and we know the following:

  • Length of mercury column (hHg) = 10 cm
  • Length of air column (hair) = 20 cm
  • Atmospheric pressure (Patm) = 75 cm of mercury

When the tube is inverted, the pressure exerted by the mercury column will change the height of the air column. The total pressure exerted by the trapped air and the mercury column must equal the atmospheric pressure. The relationship can be expressed as:

Patm = Pair + PHg

Where:

  • Pair = height of the air column (hair)
  • PHg = height of the mercury column (hHg)

Initially, when the tube is vertical:

75 cm = hair + 10 cm

Thus, hair = 75 cm - 10 cm = 65 cm

When the tube is inverted, the mercury column will exert pressure on the air column, causing it to compress. The new height of the air column (hair') can be calculated as:

hair' = Patm - hHg

Substituting the values:

hair' = 75 cm - 10 cm = 65 cm

Thus, the length of the air column when the tube is inverted is 65 cm.

2. Length of Air Column on the Cooler Side

In the second problem, we have a sealed glass tube that is 100 cm long, with a 10 cm mercury column in the center. The air on one side is at 27°C and the other side is at 0°C. We need to find the length of the air column on the cooler side. We can use Charles's Law, which states that the volume of a gas is directly proportional to its temperature (in Kelvin) when pressure is constant.

Let:

  • V1 = volume of air at 27°C
  • V2 = volume of air at 0°C

First, convert the temperatures to Kelvin:

  • T1 = 27 + 273 = 300 K
  • T2 = 0 + 273 = 273 K

Using Charles's Law:

(V1/T1) = (V2/T2)

Let the length of the air column on the warmer side be L1 and on the cooler side be L2. The total length of the tube is 100 cm, so:

L1 + L2 + 10 cm = 100 cm

L1 + L2 = 90 cm

Substituting into Charles's Law gives:

(L1/300) = (L2/273)

From the equation L1 = 90 cm - L2, we can substitute:

((90 - L2)/300) = (L2/273)

Cross-multiplying and solving for L2 leads to:

273(90 - L2) = 300L2

24570 - 273L2 = 300L2

24570 = 573L2

L2 = 42.9 cm

Thus, the length of the air column on the cooler side is approximately 42.9 cm.

3. Length of Air Column When the Tube is Tilted

In the final scenario, we have a vertical tube with a mercury column and a trapped air column. The lengths are given as:

  • Length of mercury column (hHg) = 20 cm
  • Length of trapped air column (hair) = 43 cm
  • Atmospheric pressure = 76 cm of mercury

When the tube is tilted at an angle of 60 degrees, the volume of the air column will change due to the tilt. The pressure exerted by the mercury column remains constant, but the effective height of the air column changes. The new height of the air column (hair') can be calculated using trigonometric principles.

Using the sine of the angle:

hair' = hair * cos(60°)

Since cos(60°) = 0.5:

hair' = 43 cm * 0.5 = 21.5 cm

Therefore, when the tube is tilted at an angle of 60 degrees, the length of the air column becomes 21.5 cm.

In summary, we have calculated the lengths of the air columns in various configurations, applying principles of pressure and gas laws effectively. Each scenario illustrates how changes in position and temperature can influence