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Free Thermal Equilibrium and Heat MCQs with Answers

277 Thermal Equilibrium and Heat MCQs from Physics, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.

Thermal equilibrium means that bodies in contact have the same temperature and no net heat flows between them. The topic distinguishes heat from temperature, uses the zeroth law of thermodynamics, and covers heat transfer, specific heat capacity, thermal expansion and the conditions for reaching equilibrium.

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277 questions · page 13 of 14

241. By reducing the absolute temperature of a black body to half, the total energy radiated will be:

  • A. 4
  • B. 16
  • C. 1/4
  • D. 1/16

Explanation: The total energy radiated by a black body is governed by the Stefan-Boltzmann law.

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Correct answer: 1/16

242. The second law of thermodynamics deals with conversion of heat into work and direction of

  • A. Flow of heat.
  • B. Applied force.
  • C. Applied pressure.
  • D. Flow of internal energy.

Explanation: The second law of thermodynamics is fundamentally about the direction of processes.

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Correct answer: Flow of heat.

243. When an ideal gas is cooled at constant volume until the pressure becomes half of the originalpressure, then the average translational kinetic energy of the gas molecules

  • A. Remains unchanged.
  • B. Becomes half the original.
  • C. Becomes twice the original.
  • D. Becomes thrice the original.

Explanation: In an ideal gas, the average translational kinetic energy of the molecules is directly proportional to the absolute temperature of the…

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Correct answer: Becomes half the original.

244. All Carnot engines have zero efficiency if they are operating between two bodies with

  • A. The same temperature and the same nature of working substance.
  • B. Different temperature and the same nature of working substance.
  • C. The same temperature irrespective of the nature of working substance.
  • D. Different temperatures irrespective of the nature of working substance.

Explanation: The efficiency of a Carnot engine is determined by the temperature difference between the hot and cold reservoirs.

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Correct answer: The same temperature irrespective of the nature of working substance.

245. In a thermodynamic system, if there is no change in temperature and internal energy, then the process is called an

  • A. Isobaric process.
  • B. Adiabatic process.
  • C. Isochoric process.
  • D. Isothermal process.

Explanation: The correct answer is isothermal process. In an isothermal process, the temperature of the system remains constant.

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Correct answer: Isothermal process.

246. The direction of heat flow from one object to another is based on the difference in their

  • A. density.
  • B. temperature.
  • C. specific heat.
  • D. thermal conductivity.

Explanation: B) Temperature (Correct): Heat always flows spontaneously from an object at a higher temperature to an object at a lower temperature.

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Correct answer: temperature.

247. The given observation table is used to determine the value of mechanical equivalent of heat. The electrical energy (W) consumed will be

  • A. 5 J
  • B. 10 J
  • C. 20 J
  • D. 40 J

Explanation: The electrical energy (W) consumed can be calculated using the formula:W = V × I × tWhere: * V = Potential Difference = 5 volts * I =…

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Correct answer: 20 J

248. All of the following are precautions which should be taken into consideration while measuring the mechanical equivalent of heat by electric method EXCEPT that the

  • A. supply of voltage is steady.
  • B. heating coil should be immersed in water.
  • C. calorimeter should be placed in an insulation box.
  • D. thermometer should touch the base of the calorimeter.

Explanation: D) Thermometer should touch the base of the calorimeter: This is not a precaution; in fact, it's something to avoid.

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Correct answer: thermometer should touch the base of the calorimeter.

249. The amount of heat energy needed to raise the temperature of 1 kg of a substance through 1 K is called

  • A. specific heat
  • B. heat capacity.
  • C. heat of fusion
  • D. heat of vapourisation

Explanation: A) Specific heat: This term (also known as specific heat capacity) is defined as the amount of heat energy required to raise the…

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Correct answer: specific heat

250. The gas is at its highest temperature at point(s)

  • A. ii only.
  • B. iv only.
  • C. i and ii.
  • D. iii and v.

Explanation: Based on the ideal gas law, PV = nRT, temperature (T) is directly proportional to the product of pressure (P) and volume (V) (T ∝ PV)…

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Correct answer: iv only.

251. In an experiment of measuring the mechanical equivalent of heat, a stirrer is placed in the calorimetre filled with hot water.After some time, the exposed end of the stirrer becomes hot.The process(es) that is/ are mainly involved in the transferring of heat processes is/ areI. radiationII. convectionIII. conduction

  • A. I only.
  • B. III only
  • C. I and II.
  • D. II and III.

Explanation: Convection:The hot water in the calorimeter transfers heat to the stirrer through convection, as the warmer water rises and cooler water…

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Correct answer: II and III.

252. A student touches the metal surface of a hot calorimetre. He is likely to burn his hand. If he holds his hand in the hot air inside the calorimetre, then he will remain fine. Which of the following statements BEST describe the given condition?

  • A. Both the metal and air are poor conductor of heat.
  • B. Both the metal and air are good conductors of heat.
  • C. Metal is a good conductor, but air is a poor conductor of heat.
  • D. Air is a good conductor, but metal is a poor conductor of heat.

Explanation: The problem describes a scenario where touching the metal surface of a hot calorimeter causes a burn, but holding a hand in the hot air…

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Correct answer: Metal is a good conductor, but air is a poor conductor of heat.

253. In a process the density of gas remains constant. If the temperature is doubled, then the change in the pressure will be:

  • A. 100% increase
  • B. 200% increase
  • C. 50% decrease
  • D. 25% decrease

Explanation: In an ideal gas where the density remains constant, the relationship between pressure (P), volume (V), and temperature (T) is given by the…

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Correct answer: 100% increase

254. Which of the following changes when taken together, will result in a decrease in the pressure of an ideal gas?

  • A. Volume decreased, temperature decreased
  • B. Volume decreased, temperature increased
  • C. Volume increased, temperature decreased
  • D. Volume increased, temperature increased

Explanation: An experimental gas law that describes the relationship between pressure and volume of a confined (Boyle's Law).

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Correct answer: Volume increased, temperature decreased

255. Lower fixed point of Celcius scale:

  • A. 32°C
  • B. 100°C
  • C. 273°C
  • D. 0°C

Explanation: The Celsius scale has an upper fixed point and a lower fixed point. The upper fixed point is 100°C and the lower fixed point is 0°C.

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Correct answer: 0°C

256. A frictionless heat engine can be 100% if:

  • A. The temperature of the sink is 0°C.
  • B. The temperature of the sink is 0 K.
  • C. The temperature of the source is 0.
  • D. The temperature of the sink is equal to the temperature of the source.

Explanation: Heat engines can't achieve 100% thermal efficiency according to the Second law of thermodynamics.

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Correct answer: The temperature of the sink is 0 K.

257. Radiation emitted by hot bodies have the color:

  • A. Red
  • B. Green
  • C. Blue
  • D. White

Explanation: Its color depends only on its temperature. By definition, a black body does not reflect light, and only emits light by radiation because…

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Correct answer: White

258. A liquid has mass m and specific heat capacity c. The rate of change in temperature of the liquid is R. What is the rate at which heat is transferred from the liquid?

  • A. Rmc
  • B. R/me
  • C. me/R
  • D. Rm/c

Explanation: We know that Q = mcΔTDividing both sides of the equation by time gives:Q/t = mcΔT/tQ/t = rate of heat transferΔT/t = RTherefore: rate of…

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Correct answer: Rmc

259. Woolen clothes keep the body warm because of:

  • A. Bad conductivity
  • B. Good conductivity
  • C. Low temperature
  • D. None of these options are correct

Explanation: Since air is a bad conductor of heat, it prevents the loss of heat from the body, thus keeping it warm.

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Correct answer: Bad conductivity

260. If the engine is supposed to work between 727°C and 227°C, then the maximum possible efficiency is:

  • A. 1/2
  • B. 1/4
  • C. 3/4
  • D. 1

Explanation: T1 = 727 + 273 = 1000 K T2 = 227 + 273 = 500 K Efficiency of engine = 1 - (T2/T1) = 1 - (500/1000) = 1 - ½ = ½ Hence, option A is the…

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Correct answer: 1/2
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