The working principle of refrigerator is based on the

Correct — B, second law of thermodynamics. A refrigerator moves heat from a cold interior to a warmer kitchen, which is the direction heat will never take on its own; the Clausius statement of the second law says exactly that no device can transfer heat from a colder to a hotter body without some external work being done. The compressor supplies that work, and the second law also sets the ceiling on how well the machine can do it, through the coefficient of performance, which cannot exceed the reversible value determined by the two temperatures. The first law is obeyed too, but it merely balances the energy books and would permit a refrigerator needing no power at all.

• (a)first law of thermodynamics — The first law is conservation of energy: the heat delivered to the room equals the heat taken from the cabinet plus the work supplied. It is satisfied by a refrigerator, but it does not explain why any work is needed, and a machine that cooled without power would not violate it.
• (c)Planck's radiation law — Planck's law gives the spectral distribution of radiation emitted by a black body at a given temperature. It belongs to quantum theory and radiation physics and has nothing to do with the vapour-compression cycle.
• (d)Rayleigh-Jeans law — The Rayleigh-Jeans law is the classical approximation to black-body radiation that fails at short wavelengths — the ultraviolet catastrophe that Planck's law resolved. Again a radiation law, not a refrigeration principle.

A refrigerator is a heat engine run backwards. Work is supplied to a compressor; a refrigerant absorbs heat from inside the cabinet as it evaporates at low pressure, is compressed, and then gives that heat plus the compressor's work to the room as it condenses. The second law of thermodynamics is what makes the work compulsory. In its Clausius form it forbids the spontaneous flow of heat from cold to hot; in its Kelvin-Planck form it forbids an engine that converts heat wholly into work. The efficiency measure for a refrigerator is the coefficient of performance, the heat removed divided by the work supplied, and it falls as the temperature difference grows.

Two of the four options are laws of radiation and can be discarded on sight, which leaves the real question — first law or second. The test is to ask what each law forbids. The first law forbids only the creation of energy, so a refrigerator that ran on nothing would not offend it; the second law forbids exactly the thing a refrigerator is trying to do without help, and that is why a plug and a compressor are needed. This card marks a different letter from the answer we hold on file for this question.

• The Clausius statement of the second law forbids heat flowing from a colder to a hotter body without external work.
• A refrigerator is a heat pump: work in, heat moved from the cold interior to the warmer surroundings.
• Its performance is measured by the coefficient of performance, not by efficiency.
• The first law only requires that heat rejected equals heat absorbed plus work done.
• Planck's law and the Rayleigh-Jeans law both describe black-body radiation, not thermodynamic cycles.

• Choosing the first law because energy conservation is obviously true of a refrigerator; being true is not the same as being the governing principle.
• Assuming the interior is cooled by 'creating cold'; heat is removed and dumped outside, which is why the back of the machine is warm.
• Being distracted by two radiation laws that belong to a different chapter.

A which-principle item with two irrelevant options and one plausible one, so the discrimination is entirely between the first and second laws.

No directly related past PYQ was found.

• practice — not a real PYQ

  A refrigerator transfers heat from a cold body to a hot body. This is possible because

  • (a)heat naturally flows from cold to hot
  • (b)external work is supplied by the compressor
  • (c)the first law of thermodynamics is violated
  • (d)the refrigerant has negative heat capacity

  Answer(b) external work is supplied by the compressor — the second law permits the transfer only when work is done.

• practice — not a real PYQ

  The efficiency of a refrigerator is expressed by its

  • (a)thermal efficiency
  • (b)coefficient of performance
  • (c)mechanical advantage
  • (d)power factor

  Answer(b) coefficient of performance — the heat removed from the cold reservoir divided by the work supplied.