Free Energy Losses and Efficiency MCQs with Answers
22 Energy Losses and Efficiency MCQs from Physics, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.
Efficiency compares useful output energy or power with the total input, usually expressed as a percentage. The topic covers energy losses through friction, heating, resistance and sound, along with power ratings and Sankey diagrams. Efficiency is not the same as conservation of energy, because lost energy is transferred rather than destroyed.
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- A. 30%
- B. 43%
- C. 70%
- D. 143%
Explanation: Efficiency is useful output divided by total input times 100, which is 350 over 500 times 100, giving 70%.
Correct answer: 70%- A. always greater than 100 per cent
- B. the ratio of useful output energy to total input energy, expressed as a percentage
- C. the ratio of input to output
- D. equal to the power output
Explanation: Efficiency can never exceed 100 per cent, because energy is conserved and some is always lost to friction, sound and heat.
Correct answer: the ratio of useful output energy to total input energy, expressed as a percentage- A. 80 per cent
- B. 125 per cent
- C. 100 per cent
- D. 20 per cent
Explanation: Dividing 400 by 500 and multiplying by 100 gives 80 per cent, with the remaining 100 J lost mainly as heat.
Correct answer: 80 per cent- A. energy is destroyed
- B. energy is transferred to the surroundings as heat and sound by air resistance and friction at the pivot
- C. gravity weakens
- D. the mass of the bob decreases
Explanation: Energy is conserved overall, but the mechanical energy of the pendulum is gradually converted into thermal energy of the air and the…
Correct answer: energy is transferred to the surroundings as heat and sound by air resistance and friction at the pivot- A. Solar
- B. Wind
- C. Coal
- D. Hydroelectric
Explanation: Coal is a fossil fuel formed over hundreds of millions of years, so it is consumed far faster than it can be replaced and its combustion…
Correct answer: Coal- A. Wind
- B. Water
- C. Sun
- D. Moon
Explanation: Solar radiation is the primary energy input to the Earth, and wind and flowing water are themselves driven by the uneven solar heating of…
Correct answer: Sun- A. 50%
- B. 100%
- C. 23.6%
- D. 29.4%
Explanation: Carnot efficiency is η = 1 - Tc/Th, with temperatures in kelvin. Here Th = 150°C + 273 K = 423 K and Tc = 50°C + 273 K = 323 K, so η = 1 -…
Correct answer: 23.6%- A. efficiency
- B. coefficient of performance
- C. both A and B
- D. not described
Explanation: A refrigerator is assessed by its coefficient of performance, COP = heat removed from the cold space ÷ work input, rather than by…
Correct answer: coefficient of performance- A. Fusion
- B. Polymerization
- C. Crystallization
- D. Subtraction
Explanation: Polymerization joins many small molecules called monomers to form a large molecule called a polymer.
Correct answer: Polymerization- A. direct combustion
- B. fermentation
- C. both A and B
- D. none of these
Explanation: Biomass can produce fuel by direct combustion, such as burning wood or crop waste, and by fermentation, which produces fuels such as…
Correct answer: both A and B- A. 4.00
- B. 1.00
- C. 0.25
- D. Impossible to determine
Explanation: Thermal efficiency (η) is the ratio of the useful work output to the total energy input.
Correct answer: 0.25- A. 10-25%
- B. 25-30%
- C. 30-40%
- D. 40-50%
Explanation: Due to thermodynamic limitations (like the Carnot cycle) and practical losses from friction and incomplete combustion, a typical…
Correct answer: 25-30%- A. Always higher
- B. Always lower
- C. Equal
- D. Sometimes higher
Explanation: A real heat engine has irreversibilities (e.g., friction, heat loss), making its efficiency lower than that of an ideal Carnot engine…
Correct answer: Always lower- A. 10% to 20%
- B. 20% to 35%
- C. 35% to 40%
- D. 40% to 50%
Explanation: The efficiency of a diesel engine can vary depending on various factors such as the design of the engine, operating conditions, and…
Correct answer: 35% to 40%- A. 80oC ,37oC
- B. 99oC , 30oC
- C. 99oC,25oC
- D. 99oC , 37oC
Explanation: Efficiency of Engine , = Work / QinputAs, W = 1 / 6 Qinput = 1 / 6Also, = 1 - T2 / T1WhereT1 and T2 are the temperatures of the source and…
Correct answer: 99oC , 37oC- A. 10%
- B. 20%
- C. 30%
- D. 50%
- E. 70%
Explanation: The maximum theoretical efficiency of the system is the one corresponding to the efficiency of a Carnot cycle operating between the same…
Correct answer: 50%- A. 4.00
- B. 1.00
- C. 0.25
- D. Impossible to determine
Explanation: Efficiency= Output work/ Input workAs input energy is 4 times the useful work done. Efficiency=¼=0.25Hence,C is the correct option.
Correct answer: 0.25- A. 10% to 20%
- B. 20% to 35%
- C. 35% to 40%
- D. 40% to 50%
Explanation: c) 35% to 40%:Option (c) "35% to 40%" is also a possible range of efficiency percentages for certain advanced and well-optimized diesel…
Correct answer: 35% to 40%- A. 1/2
- B. 1/4
- C. 3/4
- D. 1
Explanation: Option A is correct since the formula of efficiency for a heat engine is 1-(T2/T1).
Correct answer: 1/2- A. 50%
- B. 25%
- C. 12.5%
- D. 6.25%
Explanation: Boiling point of water= 100° =373KFreezing point of water=0° = 273KThe formula for efficiency; =1-TCold/Thotx100 = 1- 273/373x100 =26.80%…
Correct answer: 25%Energy Losses and Efficiency MCQs: common questions
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