30 Questions
What is the thermal resistance of a body a measure of?
Its opposition to the flow of heat through it
What is the significance of the Wiedemann-Franz law?
It states that a substance with high thermal conductivity has high electrical conductivity
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
What is the dimension of thermal resistance?
m^2K/W
What is the purpose of the gauze in Davy's safety lamp?
To prevent the flame from spreading
What is the unit of diffusivity?
m^2/sec
What is the rate of flow of heat called?
Heat current
What is the thermal resistance of a conductor defined as?
KA/l
In a series combination of n slabs, what is the equivalent thermal resistance?
R = l1/K1A + l2/K2A + ... + ln/KnA
Why do birds swell their feathers in winter?
To enclose more air and reduce heat loss
Why do birds feel warmer in winter?
Their feathers trap a layer of air, which is a poor conductor of heat
What is the purpose of wire gauze in a Bunsen burner setup?
To provide a pathway for heat conduction to the flask
Why are cooking utensils provided with wooden handles?
To prevent the heat from being conducted to the hand
Why do we feel warmer in a fur coat?
The air trapped in the fur coat is a poor conductor of heat, preventing body heat from being lost
What is the condition for steady-state heat flow?
The heat current is the same in all conductors
What is the physical quantity that is proportional to the surface area of a body and its excess temperature over its surroundings?
Heat current
If K1 and K2 are the thermal conductivities of two slabs of equal area, what is the equivalent thermal conductivity?
(K1 + K2) / 2
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?
dy/dt = Kθ / ρL
What is the physical quantity that depends on the properties of a fluid such as density, viscosity, specific heat, and thermal conductivity?
Convection coefficient
What is the physical phenomenon that occurs when the atmospheric temperature drops below 0°C, resulting in the growth of ice on a lake?
Freezing
What is the ratio of time taken to double and triple the thickness of ice?
1:4:9
What is the primary reason for the decrease in rate of increase of thickness of ice on ponds with time?
Ice is a poor conductor of heat
In which direction does natural convection take place?
From bottom to top
What is the mode of heat transfer by means of migration of material particles of a medium called?
Convection
What is the outcome when heating is done from the base and cooling from the top in natural convection?
Warm air moves upwards and cool air downwards
What is the correct expression for the thermal resistance of a composite slab consisting of n slabs of equal length?
Rs = 1 / (1/K1 + 1/K2 +... + 1/Kn)
In a double-walled ice house, what is the primary function of the air enclosed in between the walls?
To reduce heat transfer by conduction
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?
(θ1 - θ2) / (l1 + l2)
What is the relation between the thermal conductivity K and the melted length l in Searle's experiment?
K ∝ l^2
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?
Q = K A (θ1 - θ2) / l
Test your understanding of heat transfer and ice formation on a lake's surface. Questions cover the relationship between atmospheric temperature, ice thickness, and heat escape through the ice layer.
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