Practice Problems
Heat Transfer Methods
Directions:
On this worksheet you will investigate properties of
the three heat transfer methods
.
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Question 1
Which method of heat transfer involves actual particles circulating from one region to another?
convection
conduction
radiation
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Question 2
Which heat transfer method can take place without a medium, that is, in a vacuum?
radiation
convection
conduction
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Question 3
Newton's Law of Cooling allows us to calculate the rate at which the temperature difference between a hot object and the ambient room temperature changes with the passage of time. T
_{diff}
= T
_{o}
e
^{-kt}
. At time t = 0, the original temperature difference between a hot solid and the ambient room temperature is 54.7 ºC. If the temperature difference drops to half that value in 23.5 seconds, what is the value of the decay constant, k?
0.0339 per second
0.0426 per second
0.0316 per second
0.0295 per second
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Question 4
At what time will the temperature difference equal 9.3ºC?
90.1 sec
35.3 sec
60.1 sec
37.8 sec
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Question 5
An incandescent black body has a peak wavelength of 525 nm when its temperature is 5524 Kelvin. What would be the temperature of a second blackbody radiator that has a peak wavelength of 341.25 nm?
8498 Kelvin
10150 Kelvin
3590 Kelvin
5708 Kelvin
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Question 6
Compare the rate at which energy is given off by the second black body in Question #5 which has a peak wavelength of 341.25 nm to the first black body which has a peak wavelength of 525 nm.
2.4 : 1
5.6 : 1
1.5 : 1
1.1 : 1
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Question 7
If two other incandescent solids are at the same temperature, but one has a surface area that is 5 times greater, how would the radiant power of the larger black body compare to the rate at which energy is emitted by the smaller black body?
it would be 625 times greater
it would be 25 times greater
it would be 1.50 times smaller
it would be 5 times greater
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Question 8
One end of a 54.7-cm copper rod (
a
= 385 W/mK) is placed in 100 grams of cold water at a temperature of 4.7 ºC. The other end is placed in the flame of a bunsen burner at a temperature of 971 ºC. If the rod has a radius of 0.5 cm, then what is the initial rate at which heat is conducted along the rod?
13.9 J/sec
53.4 J/sec
68.5 J/sec
21.4 J/sec
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Question 9
If a second copper rod has the same length as the rod in Question #8 but has a radius of 0.085 cm, how would the rate of conductivity be changed?
it would decease by a factor of 0.170
it would increase by a factor of 35
it would decease by a factor of 0.0289
it would increase by a factor of 6
it would not change
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Question 10
If a third copper rod has the same radius as the rod in Question #8, but a length of 76.58 cm, how would the rate of conductivity be changed?
it would be 60% as great
it would be 16.0% as great
it would be 2.5% as great
it would be 40% as great
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Question 11
A 350 watt immersion heater is used to heat a cup of water containing 192 grams of water and a piece of ice. The cup is made of styrofoam which is an insulator and does not give up or receive heat. If it takes 3.17 minutes for the heater to bring the contents of the cup from 0ºC to 65ºC, how much ice was originally present? Here are some constants: c
_{ice}
= 2093 J/kgºC, c
_{water}
=4186 J/kgºC, L
_{f}
= 334 kJ/kg
52.3 grams
37.3 grams
66.1 grams
23.5 grams
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