Transmission of Heat
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Questions and Answers

What is the thermal resistance of a body a measure of?

  • Its ability to retain heat
  • Its ability to generate heat
  • Its opposition to the flow of heat through it (correct)
  • Its ability to conduct heat

    • What is the significance of the Wiedemann-Franz law?

  • It states that thermal conductivity is independent of electrical conductivity
  • It states that a substance with high thermal conductivity has low electrical conductivity
  • It states that electrical conductivity is independent of thermal conductivity
  • It states that a substance with high thermal conductivity has high electrical conductivity (correct)

    • Why are two thin blankets warmer than one blanket of their combined thickness?

  • The layer of air enclosed in between the two blankets reduces heat flow (correct)
  • The layer of air enclosed in between the two blankets increases heat flow
  • The two blankets have a lower thermal conductivity than the single blanket
  • The two blankets have a higher thermal conductivity than the single blanket

    • What is the dimension of thermal resistance?

    <p>m^2K/W</p> Signup and view all the answers

    What is the purpose of the gauze in Davy's safety lamp?

    <p>To prevent the flame from spreading</p> Signup and view all the answers

    What is the unit of diffusivity?

    <p>m^2/sec</p> Signup and view all the answers

    What is the rate of flow of heat called?

    <p>Heat current</p> Signup and view all the answers

    What is the thermal resistance of a conductor defined as?

    <p>KA/l</p> Signup and view all the answers

    In a series combination of n slabs, what is the equivalent thermal resistance?

    <p>R = l1/K1A + l2/K2A + ... + ln/KnA</p> Signup and view all the answers

    Why do birds swell their feathers in winter?

    <p>To enclose more air and reduce heat loss</p> Signup and view all the answers

    Why do birds feel warmer in winter?

    <p>Their feathers trap a layer of air, which is a poor conductor of heat</p> Signup and view all the answers

    What is the purpose of wire gauze in a Bunsen burner setup?

    <p>To provide a pathway for heat conduction to the flask</p> Signup and view all the answers

    Why are cooking utensils provided with wooden handles?

    <p>To prevent the heat from being conducted to the hand</p> Signup and view all the answers

    Why do we feel warmer in a fur coat?

    <p>The air trapped in the fur coat is a poor conductor of heat, preventing body heat from being lost</p> Signup and view all the answers

    What is the condition for steady-state heat flow?

    <p>The heat current is the same in all conductors</p> Signup and view all the answers

    What is the physical quantity that is proportional to the surface area of a body and its excess temperature over its surroundings?

    <p>Heat current</p> Signup and view all the answers

    If K1 and K2 are the thermal conductivities of two slabs of equal area, what is the equivalent thermal conductivity?

    <p>(K1 + K2) / 2</p> Signup and view all the answers

    What is the rate of growth of ice in a lake in terms of the thermal conductivity K, temperature θ, and latent heat of fusion L?

    <p>dy/dt = Kθ / ρL</p> Signup and view all the answers

    What is the physical quantity that depends on the properties of a fluid such as density, viscosity, specific heat, and thermal conductivity?

    <p>Convection coefficient</p> Signup and view all the answers

    What is the physical phenomenon that occurs when the atmospheric temperature drops below 0°C, resulting in the growth of ice on a lake?

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

    What is the ratio of time taken to double and triple the thickness of ice?

    <p>1:4:9</p> Signup and view all the answers

    What is the primary reason for the decrease in rate of increase of thickness of ice on ponds with time?

    <p>Ice is a poor conductor of heat</p> Signup and view all the answers

    In which direction does natural convection take place?

    <p>From bottom to top</p> Signup and view all the answers

    What is the mode of heat transfer by means of migration of material particles of a medium called?

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

    What is the outcome when heating is done from the base and cooling from the top in natural convection?

    <p>Warm air moves upwards and cool air downwards</p> Signup and view all the answers

    What is the correct expression for the thermal resistance of a composite slab consisting of n slabs of equal length?

    <p>Rs = 1 / (1/K1 + 1/K2 +... + 1/Kn)</p> Signup and view all the answers

    In a double-walled ice house, what is the primary function of the air enclosed in between the walls?

    <p>To reduce heat transfer by conduction</p> Signup and view all the answers

    What is the temperature gradient in a composite bar consisting of two conductors in series, when the heat current is the same in both conductors?

    <p>(θ1 - θ2) / (l1 + l2)</p> Signup and view all the answers

    What is the relation between the thermal conductivity K and the melted length l in Searle's experiment?

    <p>K ∝ l^2</p> Signup and view all the answers

    What is the expression for the heat current in a conductor, when the temperature difference is maintained across a rod of length l and area of cross-section A?

    <p>Q = K A (θ1 - θ2) / l</p> Signup and view all the answers

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