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?
conduction
radiation
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 64.8 ºC. If the temperature difference drops to half that value in 19.8 seconds, what is the value of the decay constant, k?
0.0350 per second
0.0505 per second
0.0286 per second
0.0299 per second
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Question 4
At what time will the temperature difference equal 15.6ºC?
29.7 sec
61.1 sec
39.2 sec
40.8 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 288.77 nm?
9570 Kelvin
6871 Kelvin
4508 Kelvin
10043 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 288.77 nm to the first black body which has a peak wavelength of 431 nm.
1.1 : 1
1.5 : 1
5.0 : 1
2.2 : 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 3 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 3 times greater
it would be 81 times greater
it would be 9 times greater
it would be 1.32 times smaller
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Question 8
One end of a 64.8-cm copper rod (
a
= 385 W/mK) is placed in 100 grams of cold water at a temperature of 3.96 ºC. The other end is placed in the flame of a bunsen burner at a temperature of 934 ºC. If the rod has a radius of 0.3 cm, then what is the initial rate at which heat is conducted along the rod?
4.1 J/sec
15.6 J/sec
10.4 J/sec
50.6 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 0.072 cm, how would the rate of conductivity be changed?
it would decease by a factor of 0.240
it would increase by a factor of 17
it would decease by a factor of 0.0576
it would not change
it would increase by a factor of 4
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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 84.89 cm, how would the rate of conductivity be changed?
it would be 3.2% as great
it would be 9.6% as great
it would be 31% as great
it would be 69% as great
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Question 11
A 350 watt immersion heater is used to heat a cup of water containing 200 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 3.16 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
55.7 grams
31.4 grams
44.1 grams
19.8 grams
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