A system that does NOT allow exchange of heat with its surrounding is called
- A.Adiabatic system
- B.Non-adiabatic system
- C.Equilibrium system
- D.Non-equilibrium system
Correct answer
Explanation
The correct answer is A, Adiabatic system. A system whose walls let no heat pass in or out is called adiabatic, so any change in its state happens with zero heat exchange (Q = 0).
In an adiabatic process the first law of thermodynamics reduces to ΔU = −W: the work done by or on the gas changes its internal energy and so its temperature. That is why a gas cools when it expands suddenly and heats up when it is compressed quickly, as in a bicycle pump or a diesel engine cylinder. A well-insulated vessel such as a thermos flask comes close to an adiabatic wall; a very fast process also behaves adiabatically because heat has no time to flow.
B is wrong: a non-adiabatic (diathermic) wall is one that does allow heat exchange. C is wrong: equilibrium describes a state in which properties do not change, not a type of wall. D is wrong: a non-equilibrium system is simply one whose properties are still changing.
Exam tip: adiabatic means Q = 0, isothermal means constant temperature, isobaric means constant pressure and isochoric means constant volume.
Practice Questions
View allA negative work is done when an applied force F and the corresponding displacement S are
- A.perpendicular to each other.
- B.parallel to each other.
- C.anti-parallel to each other.
- D.equal in magnitude.
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Work is negative when the force acts opposite to the displacement, because the angle between them is then 180°. Work done is W = F S cos θ, where θ is the angle between the force and the displacement.
Read the full explanation →Which one of the following statements about a satellite orbiting around the Earth is correct ?
- A.Satellite is kept in orbit by remote control from ground station.
- B.Satellite is kept in orbit by retro-rocket and solar energy keeps it moving around the Earth.
- C.Satellite requires energy from solar panels and solid fuels for orbiting.
- D.Satellite does not require any energy for orbiting.
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Once a satellite is placed in orbit with the right speed, the Earth's gravity keeps it going round without any engine.
Read the full explanation →Which one of the following is not a conservative force ?
- A.Frictional force
- B.Electric force
- C.Gravitational force
- D.Spring force
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Friction is a non-conservative force because the work it does depends on the path taken and the energy it removes is lost as heat.
Read the full explanation →A microphone converts
- A.electrical signals to sound waves
- B.sound waves to electrical signals
- C.microwaves to sound waves
- D.sound waves to microwaves
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A microphone is a transducer that changes the pressure variations of sound into a matching electrical signal. In a common dynamic microphone, sound waves make a thin diaphragm vibrate.
Read the full explanation →When a light ray passes through from air to water with a non-zero angle the ray will be
- A.bending towards the normal
- B.bending away from the normal
- C.propagating in straight line
- D.reflected towards the opposite direction
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Light slows down when it enters water from air, so a ray that strikes the surface at an angle bends towards the normal.
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