An insulated, vertical piston-cylinder assembly contains 50 L of steam at 105 oC. The outside pressure is 101 kPa. The piston has a diameter of 20 cm and the combined mass of the piston and the load is 75 kg. The electrical heater and the paddle wheel are turned on and the piston rises slowly by 25 cm with a constant pressure. The total internal energy increases by 3.109 kJ. Determine:

a. The pressure of air inside the cylinder during the process.
b. The boundary work performed by the gas.
c. The combined work transfer by the shaft and electricity.

Explanation:

From the given information:

The pressure of the air during the process =

The pressure of the air during the process = 124.42 kPa

The boundary work = P × ΔW

The boundary work = 124.42  kPa × (π/4) × (0.2 m)² × 0.25 m × (1 kJ/1 kPa.m³)

The boundary work = 0.977 kJ

The combined work transfer =

The combined work transfer = 0.977 + 3.109 kJ

The combined work transfer = 4.086 kJ

speed of light in vacuum is 300,000 km/s

speed of light in other mediums is given by the expression v = c/n, where c is the speed of light in vacuum and n is the refractive index of medium.

for the first medium v = 200,000 km/s

  so, refractive index of medium = 300000/200000 = 1.5

    1.5 refractive index is usually for glass. so first medium is glass.

for the second medium v = 250,00 km/s

so, refractive index of medium = 300000/250000 = 1.2

    1.2 refractive index is usually for water. so second medium is water.

for the third medium v = 0 km/s

so, refractive index of medium = 300000/0 = ∞

    ∞ refractive index is usually for opaque mediums. so third medium is opaque medium.