Thermodynamics
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Questions and Answers

What is the ratio of useful work obtained from the engine to the heat supplied to it?

  • Work done W
  • Heat input Q1
  • Thermodynamic efficiency η (correct)
  • Heat output Q2

    • What is the result of the first law of thermodynamics for a cyclic process?

  • ΔU = Q1
  • ΔU = W
  • ΔU = Q2
  • ΔU = 0 (correct)

    • What is the fundamental principle underlying the efficiency of a Carnot engine?

  • Efficiency is directly proportional to the heat input
  • Efficiency is independent of the volume of the system
  • Heat input is always equal to work output
  • Temperatures of source and sink determine the efficiency (correct)

    • What is the characteristic of a perfect heat engine?

    <p>It converts all heat into work</p> Signup and view all the answers

    Which statement is a direct consequence of the second law of thermodynamics?

    <p>Whole of heat can never be converted into work</p> Signup and view all the answers

    What is the relation between the temperatures of the source and sink in a Carnot engine?

    <p>T1 &lt; T2</p> Signup and view all the answers

    What is the purpose of a refrigerator or heat pump?

    <p>To transfer heat from a cold body to a hot body</p> Signup and view all the answers

    Which statement is true about the efficiency of an actual engine?

    <p>It is always lesser than the efficiency of an ideal engine</p> Signup and view all the answers

    What is the definition of the efficiency of a heat engine?

    <p>η = W / Q1</p> Signup and view all the answers

    What is the condition for a reversible heat engine to be equally efficient?

    <p>It must work between the same temperatures</p> Signup and view all the answers

    What is the coefficient of performance of a perfect refrigerator?

    <p>∞</p> Signup and view all the answers

    What is the relation between the coefficient of performance and the efficiency of a refrigerator?

    <p>β = 1 - η</p> Signup and view all the answers

    What is the condition for the coefficient of performance to be zero?

    <p>T2 = 0</p> Signup and view all the answers

    What does the first law of thermodynamics explain?

    <p>The equivalence of work and heat</p> Signup and view all the answers

    What is the expression for the coefficient of performance of a Carnot refrigerator?

    <p>β = (Q1 - Q2) / (T1 - T2)</p> Signup and view all the answers

    What is the approximate height a person can climb if they gain 105 calories of heat energy from food and their body's efficiency is 28%?

    <p>200 m</p> Signup and view all the answers

    If a hailstone at 0°C falls from a height of 1 km on an insulating surface, converting its kinetic energy into heat, what fraction of it will melt?

    <p>1/33</p> Signup and view all the answers

    A bullet moving with a uniform velocity stops suddenly after hitting a target and its whole mass melts. If the initial temperature is 25°C, the melting point is 475°C, and the latent heat is L, what is the correct equation?

    <p>ms(475 - 25) + mL = mv^2/2</p> Signup and view all the answers

    What is the unit of the energy required to melt a certain amount of substance?

    <p>calorie/kg</p> Signup and view all the answers

    If a person's body is at a temperature of 25°C and they gain 105 calories of heat energy from food, what is the approximate increase in their potential energy?

    <p>4.2 J</p> Signup and view all the answers

    What is the unit of mechanical equivalent of heat J?

    <p>Joule calorie⁻¹</p> Signup and view all the answers

    If a bullet of mass m and velocity v is fired from a gun and strikes a target, what is the rise in temperature of the bullet?

    <p>Δt = v² / 2Js</p> Signup and view all the answers

    What is the expression for the potential energy of water in a stream falling from a height h?

    <p>mgh</p> Signup and view all the answers

    What is the value of the mechanical equivalent of heat J in kilocalorie?

    <p>4.2 × 10³</p> Signup and view all the answers

    What is the significance of the mechanical equivalent of heat J?

    <p>It is a conversion factor that converts Joule or erg into calorie or kilocalorie</p> Signup and view all the answers

    For an ideal gas, if the pressure is constant, then what is the ratio of the heat energy used in doing external work to the total heat energy given?

    <p>40%</p> Signup and view all the answers

    What is the change in internal energy of a system if the latent heat of vaporization of water is 2240 J/g and the work done in the process of expansion of 1g is 168 J?

    <p>2072 J</p> Signup and view all the answers

    For an ideal gas, if the adiabatic index is 5/3, then what is the ratio of the specific heat at constant pressure to the specific heat at constant volume?

    <p>5/3</p> Signup and view all the answers

    If the volume of 1kg of water at 100°C is 10^(-3) m^3 and the volume of 1 kg of steam at normal pressure is 1.671 m^3, then what is the density of the steam?

    <p>0.598 kg/m^3</p> Signup and view all the answers

    If the heat given to a gas is 1050 calorie, and R = 2 cal/mole degree, then what is the change in temperature of the gas?

    <p>30°C</p> Signup and view all the answers

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