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
convection
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 60.5 ºC. If the temperature difference drops to half that value in 16.8 seconds, what is the value of the decay constant, k?
0.0595 per second
0.0413 per second
0.0242 per second
0.0282 per second
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Question 4
At what time will the temperature difference equal 15.7ºC?
49.0 sec
33.4 sec
25.2 sec
32.6 sec
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Question 5
An incandescent black body has a peak wavelength of 480 nm when its temperature is 6042 Kelvin. What would be the temperature of a second blackbody radiator that has a peak wavelength of 388.8 nm?
6133 Kelvin
4894 Kelvin
7459 Kelvin
5510 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 388.8 nm to the first black body which has a peak wavelength of 480 nm.
1.5 : 1
1.2 : 1
1.1 : 1
2.3 : 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 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 1.50 times smaller
it would be 5 times greater
it would be 25 times greater
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Question 8
One end of a 60.5-cm copper rod (
a
= 385 W/mK) is placed in 100 grams of cold water at a temperature of 3.36 ºC. The other end is placed in the flame of a bunsen burner at a temperature of 959 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?
12.4 J/sec
76.6 J/sec
19.1 J/sec
47.8 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 0.13 cm, how would the rate of conductivity be changed?
it would decease by a factor of 0.0676
it would not change
it would decease by a factor of 0.260
it would increase by a factor of 4
it would increase by a factor of 15
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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 79.86 cm, how would the rate of conductivity be changed?
it would be 68% as great
it would be 10.2% as great
it would be 32% as great
it would be 3.1% as great
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Question 11
A 350 watt immersion heater is used to heat a cup of water containing 183 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 2.86 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
37.4 grams
16.8 grams
47.3 grams
26.7 grams
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