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(Coefficient of thermal conductivity of glass is 2.2x10 cal s cm K )
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8 (a)What are the three modes of transfer of heat?
(b)Define temperature gradient.
9 A brass wire 1.8 m long at 27 °C is held taut with little tension between two rigid supports. If the
wire is cooled to a temperature of – 39 °C, what is the tension developed in the wire, if its diameter
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is 2.0 mm ? Co-efficient of linear expansion of brass = 2.0 x 10 K ; Young’s modulus of brass =
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0.91 x 10 Pa
10 (a) The triple-point of water is a standard fixed point in modem thermometry. Why ? What is wrong
in taking the melting point of ice and the boiling point of water as standard fixed points (as was
originally done in the Celsius scale) ?
(b) There were two fixed points in the original Celsius scale as mentioned above which were
assigned the number 0 °C and 100 °C respectively. On the absolute scale, one of the fixed points
is the triple-point of water, which on the Kelvin absolute scale is assigned the number 273.16 K.
What is the other fixed point on this (Kelvin) Scale ?
11 A 10 kW drilling machine is used to drill a bore in a small aluminium block of mass 8.0 kg. How
much is the rise in temperature of the block in 2.5 minutes, assuming 50% of power is used up in
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heating the machine itself or lost to the surroundings? Specific heat of aluminium = 0.91 J g K .
12 Explain why:
(a) a body with large reflectivity is a poor emitter.
(b) a brass tumbler feels much colder than a wooden tray on a chilly day.
13 Describe some of the phenomena which are based on thermal convections.
14 (a)What is regelation?
(b)Give one practical application of regelation.
15 (a)Define Latent heat of fusion.
(b)Define Latent heat of vaporization.
16 Explain the importance of Greenhouse effect?
17 Explain why:
(a) an optical pyrometer (for measuring high temperatures) calibrated for an ideal black body
radiation gives too low a value for the temperature of a red hot iron piece in the open, but gives a
correct value for the temperature when the same piece is in the furnace.
