practice_exam_1

# practice_exam_1 - Midterm Exam PHYS 1220 Sum09(your name 8...

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1- A long copper rod, 1[m] long and of rectangular cross sectional area (side a has length 4[cm] and side b has length 2[cm]), is insulated to the sides and its ends stick in two water baths. One water bath is at 80°C and the rod is at 40°C when thermal equilibrium has been reached. a) What is the rate of heat flow, dQ/dt, into the second water bath, if its temperature is 20°C? Hint: Use k Cu = 400[W/mK] b) A lightbulb filament is cylindrical. Its radius is [cm] and its length is 2[cm]. How much does the thermal heat radiation of the bulb change when the filament temperature rises from 1000°K to 1200°K, while the temperature of the environment changes from 300°K to 400°K? (Assume that the temperature of the environment rises because of the heat radiation of the filament – the bulb is mounted in a small enclosure.) Hint: Assume that the filament is a perfect blackbody. Leave the value of the Stefan-Boltzmann constant as σ in the equation.
2- An insulated beaker is kept at temperature 30[°C]. It holds 0.4[kg] of hot water, which is initially at 60[°C]. How many kilograms of ice at -20[°C] must be dropped into the tea to make ‘ice tea’ at 10[°C]? Hint: Use c wat = 4200 []/kgK] c ice = 2100 [J/kgK] L wat-ice = 3 10 3 [J/kg] Assume that the water will first come to an equilibrium with the beaker and then with the ice.

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3- A flask contains H 2 O vapor at 120°C.
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• Fall '10
• Feiguin
• Miami, Fundamental physics concepts

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