A brass scale of a barometer gives correct reading at 0°C. αBrass = 0...
Suppose the correct barometer height at 0°C is (l
0, then
l0 + Δl = 75
or l0 +75 x (αHg ~αb) x 27 = 75
or l0 + 75 x (0.6 x 10-4 - 0.2 x 10-4) x 27 = 75
∴ l0 = 74.92 cm
A brass scale of a barometer gives correct reading at 0°C. αBrass = 0...
To solve this problem, we need to consider the expansion of the brass scale and how it affects the reading on the barometer.
1. Understanding the problem:
- The brass scale of the barometer gives correct readings at 0°C.
- The coefficient of linear expansion for brass (αBrass) is given as 0.00002/°C.
- The barometer reads 75 cm at 27°C.
- We need to find the atmospheric pressure at 0°C.
2. Calculating the expansion of the brass scale:
- The change in length of the brass scale can be calculated using the formula: ΔL = αL₀ΔT
where ΔL is the change in length, α is the coefficient of linear expansion, L₀ is the initial length, and ΔT is the change in temperature.
- Here, the initial length of the scale (L₀) is 75 cm and the change in temperature (ΔT) is 27°C.
- Substituting the values, we get: ΔL = (0.00002/°C)(75 cm)(27°C)
- Simplifying, we find: ΔL = 0.0405 cm
3. Adjusting the barometer reading:
- Since the brass scale expands with temperature, the length of the scale increases as the temperature rises.
- Therefore, the barometer reading at 27°C includes the expansion of the scale.
- To find the actual atmospheric pressure at 0°C, we need to subtract the expansion of the scale from the given reading at 27°C.
- The corrected length of the scale at 27°C is: L_corrected = L_reading - ΔL
- Substituting the values, we have: L_corrected = 75 cm - 0.0405 cm = 74.9595 cm
4. Converting the corrected length to atmospheric pressure:
- The atmospheric pressure is directly proportional to the height of the mercury column in the barometer.
- Therefore, we can say that the atmospheric pressure at 0°C is directly proportional to the corrected length of the scale at 27°C.
- Let's assume the atmospheric pressure at 0°C is P₀.
- Using the proportional relationship, we can write: P₀/P_reading = L_corrected/L_reading
- Substituting the values, we get: P₀/75 cm = 74.9595 cm/75 cm
- Simplifying, we find: P₀ = (74.9595 cm * 75 cm) / 75 cm = 74.9595 cm
5. Final answer:
- The atmospheric pressure at 0°C is approximately 74.92 cm, which corresponds to option 'C'.
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