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?
radiation
conduction
convection
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Question 2
Which heat transfer method can take place without a medium, that is, in a vacuum?
convection
radiation
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 59.2 ºC. If the temperature difference drops to half that value in 23.4 seconds, what is the value of the decay constant, k?
0.0427 per second
0.0315 per second
0.0296 per second
0.0338 per second
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Question 4
At what time will the temperature difference equal 14.8ºC?
45.5 sec
46.8 sec
35.1 sec
70.2 sec
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Question 5
An incandescent black body has a peak wavelength of 633 nm when its temperature is 4581 Kelvin. What would be the temperature of a second blackbody radiator that has a peak wavelength of 360.81 nm?
8037 Kelvin
12470 Kelvin
4854 Kelvin
2611 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 360.81 nm to the first black body which has a peak wavelength of 633 nm.
9.5 : 1
3.1 : 1
1.8 : 1
1.2 : 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 5 times greater
it would be 625 times greater
it would be 25 times greater
it would be 1.50 times smaller
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Question 8
One end of a 59.2-cm copper rod (
a
= 385 W/mK) is placed in 100 grams of cold water at a temperature of 4.68 ºC. The other end is placed in the flame of a bunsen burner at a temperature of 987 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?
13.0 J/sec
50.2 J/sec
20.1 J/sec
72.9 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 0.125 cm, how would the rate of conductivity be changed?
it would decease by a factor of 0.250
it would increase by a factor of 16
it would increase by a factor of 4
it would decease by a factor of 0.0625
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 81.70 cm, how would the rate of conductivity be changed?
it would be 14.4% as great
it would be 2.6% as great
it would be 62% as great
it would be 38% as great
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Question 11
A 350 watt immersion heater is used to heat a cup of water containing 212 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 3.42 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
52.1 grams
37.1 grams
65.9 grams
23.4 grams
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