The working principle of refrigerator is based on the
- A.first law of thermodynamics
- B.second law of thermodynamics
- C.Planck's radiation law
- D.Rayleigh-Jeans law
Correct answer
Explanation
The correct answer is B, second law of thermodynamics. A refrigerator moves heat from a cold space to a warmer room, which never happens on its own, and the second law explains what it takes to make it happen.
The Clausius statement of the second law says heat cannot flow by itself from a colder body to a hotter one. A refrigerator overcomes this by using external work: the compressor, driven by electricity, pumps a refrigerant through a cycle in which it absorbs heat inside the cabinet as it evaporates and releases heat outside through the coils at the back. It is a heat engine run in reverse, and its efficiency is described by the coefficient of performance.
A is wrong because the first law only states energy conservation and does not explain the direction of heat flow. C is wrong because Planck's law describes the radiation emitted by a black body. D is wrong because the Rayleigh-Jeans law is an old classical approximation of black-body radiation.
Exam tip: refrigerator and heat pump = second law (Clausius statement); conservation of energy = first law.
Practice Questions
View allThe potential difference between the terminals of an electrical heating device is 40 V, when it draws a current of 2 A from the source. Which one of the following is the correct value of current drawn by the heating device if the potential is increased to 140 V?
- A.7 A
- B.5 A
- C.4 A
- D.2 A
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By Ohm's law the heater's resistance is 40 V divided by 2 A, which is 20 ohms, so at 140 V it draws 140 divided by 20, or 7 A. Ohm's law states that, at constant temperature, the current through a conductor is directly proportional to the potential difference across…
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- A.1 only
- B.2 only
- C.Both 1 and 2
- D.Neither 1 nor 2
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Read the full explanation →Which one among the following statements related to human eye is correct?
- A.For a person suffering from short-sight defect, the image of a distant object is focused behind the retina.
- B.Short-sight defect can be corrected by a converging spectacle lens.
- C.For a person suffering from long-sight defect, the image of a near object is focused behind the retina.
- D.Long-sight defect can be corrected by a diverging spectacle lens.
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Read the full explanation →When sunlight (white light) falls on a triangular glass prism, a band of colours called a spectrum is obtained. Which one among the following represents this effect appropriately?
- A.Reflection
- B.Diffraction
- C.Refraction
- D.Dispersion
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Read the full explanation →Which one of the following statements is correct?
- A.The number of electrons in alpha particle is 2.
- B.The coordination number of EDTA is 6.
- C.The charge of beta (β) particle is +2.
- D.Both carbon and silicon form ionic compounds.
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EDTA is a hexadentate ligand: one EDTA ion binds a metal ion through six donor atoms, so it forms complexes with coordination number 6.
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