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Chapter 15: 8MCQ (page 412)

On a very hot day, could you cool your kitchen by leaving the refrigerator door open?

(a) Yes, but it would be very expensive.

(b) Yes, but only if the humidity is below 50%.

(c) No, the refrigerator would exhaust the same amount of heat into the room as it takes out of the room.

(d) No, the heat exhausted by the refrigerator into the room is more than the heat the refrigerator takes out of the room.

Short Answer

Expert verified

The correct option is (d).

Step by step solution

01

Principle of refrigerator

A refrigerator is a device to cool a lower temperature region by extracting heat from that region.

By doing work, heat is taken out from a low-temperature region (such as inside a refrigerator), and a greater amount of heat is exhausted to a high-temperature region (the room).

02

Explanation

On a very hot day, if you open your refrigerator door, it will not be possible to cool the whole kitchen because the heat exhausted by the refrigerator into the room is more than the heat the refrigerator takes out of the room.

Hence, option (d) is correct.

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Most popular questions from this chapter

A 38% efficient power plant puts out 850 MW of electrical power. Cooling towers take away the exhaust heat.

(a) If the air \(\left( {{\bf{k}}{{\bf{m}}{\bf{3}}}} \right)\) temperature is allowed to rise by 7.0掳C, estimate what volume of air is heated per day. Will the local climate be heated significantly?

(b) If the heated air were to form a layer 180 m thick, estimate how large an area it would cover for 24 h of operation. Assume the air has a density of \({\bf{1}}{\bf{.3 kg/}}{{\bf{m}}{\bf{3}}}\) and a specific heat of about \({\bf{1}}{\bf{.0}}{\rm{ }}{\bf{kJ/kg}} \cdot {\bf{\circ C}}\) at constant pressure.

Question: (a) At a steam power plant, steam engines work in pairs, the heat output of the first one being the approximate heat input of the second. The operating temperatures of the first are 750掳C and 440掳C, and of the second 415掳C and 270掳C. If the heat of combustion of coal is \({\bf{2}}{\bf{.8 \times 1}}{{\bf{0}}^{\bf{7}}}\;{{\bf{J}} \mathord{\left/{\vphantom {{\bf{J}} {{\bf{kg}}}}} \right.} {{\bf{kg}}}}\) at what rate must coal be burned if the plant is to put out 950 MW of power? Assume the efficiency of the engines is 65% of the ideal (Carnot) efficiency. (b) Water is used to cool the power plant. If the water temperature is allowed to increase by no more than 4.5 C掳, estimate how much water must pass through the plant per hour.

Question:(II) A heat engine exhausts its heat at 340掳C and has a Carnot efficiency of 36%. What exhaust temperature would enable it to achieve a Carnot efficiency of 42%?

Question: (II) How much less per year would it cost a family to operate a heat pump that has a coefficient of performance of 2.9 than an electric heater that costs \(2000 to heat their home for a year? If the conversion to the heat pump costs \)15,000, how long would it take the family to break even on heating costs? How much would the family save in 20 years?

A heat engine operates between a high temperature of about 600掳C and a low temperature of about 300掳C. What is the maximum theoretical efficiency for this engine?

(a) \( = 100\% \). (b) \( \approx 66\% \). (c) \( \approx 50\% \). (d) \( \approx 34\% \).

(e) Cannot be determined from the given information.
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