An ideal gas enclosed in a vertical cylindrical container supports a freely moving piston of mass M. The piston and the cylinder have equal cross sectional area A. When the piston is in equilibrium, the volume of the gas is V0 and its pressure is P0. The piston is slightly displaced from the equilibrium position and released. Assuming that the system is completely isolated from its surrounding, the piston executes a simple harmonic motion with frequency.
This problem involves an ideal gas supporting a piston that executes simple harmonic motion when displaced slightly. Let's break down the concept step by step.
Step 1: Understand the Equilibrium Condition
In equilibrium, the piston is at rest. The forces acting on the piston are:
Step 2: Analyze a Small Displacement
When the piston is displaced downward by a small distance , the volume decreases by (since cross-sectional area is A). The new volume is .
Since the system is isolated (adiabatic condition), the process is adiabatic. For an adiabatic process in an ideal gas: where is the adiabatic index.
Let the new pressure be . Then:
For small , we can use binomial approximation: (Note: Actually, for small . Here, , so )
Thus, Using binomial approximation again:
Step 3: Find the Restoring Force
The net force on the piston after displacement is: But from equilibrium, , so:
Substitute from above: So,
This net force is restoring (opposite to displacement) and proportional to . So, it represents a simple harmonic motion with spring constant:
Step 4: Find the Frequency
The angular frequency for SHM is given by:
The frequency is:
Comparing with the options, this matches the fourth option:
Final Answer: The piston executes simple harmonic motion with frequency
Simple Harmonic Motion (SHM): A type of periodic motion where the restoring force is directly proportional to the displacement and acts in the direction opposite to that of displacement. The general form is , leading to angular frequency and frequency .
Adiabatic Process: A thermodynamic process in which no heat is exchanged with the surroundings. For an ideal gas, , where is the ratio of specific heats.
Binomial Approximation: For small , . This is crucial for linearizing equations in physics problems involving small displacements.