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Physics Chapter 8 : Topic 7
Work Done by and on a Gas
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When a gas expands and pushes a piston outward, the work done is described as:
Reasoning: During expansion, the gas applies force on the piston and causes displacement. Therefore, the gas does work on the surroundings.
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A gas is compressed by an external force acting on a piston. The work involved is:
Reasoning: During compression, the external agent applies force and moves the piston inward, transferring energy to the gas. Hence, work is done on the gas.
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The sign convention for work done by a gas during expansion is:
Reasoning: In thermodynamics, expansion means gas displacement is in the same direction as the force exerted by the gas, so work done by gas is positive.
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When a gas is compressed, the work done by the gas is:
Reasoning: During compression, the displacement of the gas boundary is opposite to the force exerted by the gas, so work done by gas is negative.
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Which statement correctly distinguishes work done by a gas and work done on a gas?
Reasoning: Expansion causes the gas to perform work on surroundings, while compression involves surroundings performing work on the gas.
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A gas expands from volume $\mathbf{V}_{\mathbf{1}}$ to $\mathbf{V}_{\mathbf{2}}$ against a constant external pressure. The work done by the gas is:
Reasoning: Work done by gas is pressure multiplied by change in volume. During expansion, $\mathbf{V}_{\mathbf{2}}\mathbf{>}\mathbf{V}_{\mathbf{1}}$, making work positive.
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A gas is compressed from volume $\mathbf{4\ m}^{\mathbf{3}}$ to $\mathbf{2\ m}^{\mathbf{3}}$ under constant pressure of$\mathbf{\ }\mathbf{5\ Pa}$. The work done by the gas is:
Reasoning: $\mathbf{W = p\mathrm{\Delta}V = P}\left( \mathbf{V}_{\mathbf{2}}\mathbf{-}\mathbf{V}_{\mathbf{1}} \right)\mathbf{= 5}\left( \mathbf{2 - 4} \right)\mathbf{= 5}\left( \mathbf{- 2} \right)\mathbf{= - \ 10\ J}$Negative sign shows work is done on the gas.
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If the volume of a gas remains constant during a process, the work done by the gas is:
Reasoning: Work depends on change in volume. $\Longrightarrow$ $\mathbf{W = P\mathrm{\Delta}V}$If $\mathbf{\mathrm{\Delta}V = 0}$, no work is done.
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In a pressure-volume $\mathbf{P - V}$ diagram, the area under the curve represents:
Reasoning: The area under a $\mathbf{P - V}$ curve represents $\mathbf{W = p\mathrm{\Delta}V}$, which is the work done by or on the gas.
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During an expansion process, which energy transfer occurs?
Reasoning: The expanding gas uses its energy to push the surroundings, performing work.
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When work is done on a gas, the energy of the gas generally:
Reasoning: Compression transfers mechanical energy into the gas, increasing its internal energy if other factors remain unchanged.
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Which situation represents work done by a gas?
Reasoning: The gas exerts force and causes movement of the turbine blade, so work is done by the gas.
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Which situation represents work done on a gas?
Reasoning: The piston does work on the gas by reducing its volume.
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The mathematical expression for work done by a gas at constant pressure is:
Reasoning: At constant pressure, work done is pressure multiplied by change in volume.
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If a gas expands freely into a vacuum, the work done by the gas is:
Reasoning: In free expansion, external pressure is zero, so $\mathbf{W =}\mathbf{P}_{\mathbf{ext}}\mathbf{\ \mathrm{\Delta}V = 0}$.
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A gas receives $\mathbf{500\ J}$ of energy due to compression. This energy transfer is classified as:
Reasoning: Compression transfers mechanical energy from surroundings into the gas.
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In an expansion process, the force exerted by gas and displacement of piston are:
Reasoning: The gas pushes the piston outward, so force and displacement are in the same direction.
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A gas does $\mathbf{200\ J}$ of work while expanding. This means:
Reasoning: Positive work done by gas means the gas transfers energy to the surroundings.
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Which statement about work done on a gas is correct?
Reasoning: When surroundings compress the gas, mechanical energy is transferred into the gas.
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A piston moves inward due to external pressure on a gas. Which quantity becomes negative?
Reasoning: Since the gas is compressed, the work done by gas is negative according to thermodynamic sign convention.
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The main factor that determines whether work is done by or on a gas is:
Reasoning: Expansion indicates work by gas, while compression indicates work on gas.
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A gas expands slowly while maintaining constant pressure. Which statement is correct?
Reasoning: Expansion at constant pressure means $\mathbf{W = P\mathrm{\Delta}V}$, with positive $\mathbf{\mathrm{\Delta}V}$.
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During compression of a gas, the volume change $\mathbf{\mathrm{\Delta}V}$ is:
Reasoning: Compression reduces volume, so final volume is less than initial volume.
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A gas performs work on the surroundings when:
Reasoning: Increase in volume means the gas expands and pushes against surroundings.
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Which statement best explains the difference between work done by a gas and work done on a gas?
Reasoning: Work done by gas transfers energy from gas to surroundings, while work done on gas transfers energy from surroundings to gas.
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