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
convection
conduction
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Question 2
Which heat transfer method can take place without a medium, that is, in a vacuum?
conduction
radiation
convection
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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 52.2 ºC. If the temperature difference drops to half that value in 17.7 seconds, what is the value of the decay constant, k?
0.0255 per second
0.0287 per second
0.0565 per second
0.0392 per second
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Question 4
At what time will the temperature difference equal 8.9ºC?
45.2 sec
67.9 sec
27.9 sec
26.6 sec
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Question 5
An incandescent black body has a peak wavelength of 431 nm when its temperature is 6729 Kelvin. What would be the temperature of a second blackbody radiator that has a peak wavelength of 318.94 nm?
7540 Kelvin
9093 Kelvin
6841 Kelvin
4979 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 318.94 nm to the first black body which has a peak wavelength of 431 nm.
1.4 : 1
1.1 : 1
1.8 : 1
3.3 : 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 4 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 4 times greater
it would be 16 times greater
it would be 256 times greater
it would be 1.41 times smaller
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Question 8
One end of a 52.2-cm copper rod (
a
= 385 W/mK) is placed in 100 grams of cold water at a temperature of 3.54 ºC. The other end is placed in the flame of a bunsen burner at a temperature of 949 ºC. If the rod has a radius of 0.4 cm, then what is the initial rate at which heat is conducted along the rod?
35.1 J/sec
17.5 J/sec
9.1 J/sec
53.4 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 0.068 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 increase by a factor of 6
it would not change
it would decease by a factor of 0.0289
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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 72.56 cm, how would the rate of conductivity be changed?
it would be 61% as great
it would be 2.6% as great
it would be 39% as great
it would be 15.2% as great
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Question 11
A 350 watt immersion heater is used to heat a cup of water containing 201 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 3.12 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
28.1 grams
39.4 grams
17.7 grams
49.8 grams
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