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?
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 58.9 ºC. If the temperature difference drops to half that value in 21.6 seconds, what is the value of the decay constant, k?
0.0463 per second
0.0312 per second
0.0321 per second
0.0307 per second
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Question 4
At what time will the temperature difference equal 16.5ºC?
43.7 sec
32.4 sec
39.7 sec
59.5 sec
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Question 5
An incandescent black body has a peak wavelength of 624 nm when its temperature is 4647 Kelvin. What would be the temperature of a second blackbody radiator that has a peak wavelength of 386.88 nm?
2881 Kelvin
4885 Kelvin
11020 Kelvin
7496 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 386.88 nm to the first black body which has a peak wavelength of 624 nm.
1.6 : 1
1.1 : 1
6.8 : 1
2.6 : 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 1.32 times smaller
it would be 9 times greater
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Question 8
One end of a 58.9-cm copper rod (
a
= 385 W/mK) is placed in 100 grams of cold water at a temperature of 4.32 ºC. The other end is placed in the flame of a bunsen burner at a temperature of 1015 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?
18.7 J/sec
12.5 J/sec
42.3 J/sec
4.9 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 0.084 cm, how would the rate of conductivity be changed?
it would increase by a factor of 4
it would decease by a factor of 0.0784
it would increase by a factor of 13
it would not change
it would decease by a factor of 0.280
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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 84.23 cm, how would the rate of conductivity be changed?
it would be 18.5% as great
it would be 57% as great
it would be 2.3% as great
it would be 43% as great
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Question 11
A 350 watt immersion heater is used to heat a cup of water containing 208 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 3.32 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
34.3 grams
48.1 grams
21.6 grams
60.8 grams
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