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?
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 58.7 ºC. If the temperature difference drops to half that value in 15.6 seconds, what is the value of the decay constant, k?
0.0444 per second
0.0641 per second
0.0275 per second
0.0225 per second
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Question 4
At what time will the temperature difference equal 17.6ºC?
40.6 sec
27.1 sec
32.3 sec
23.4 sec
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Question 5
An incandescent black body has a peak wavelength of 669 nm when its temperature is 4335 Kelvin. What would be the temperature of a second blackbody radiator that has a peak wavelength of 495.06 nm?
7540 Kelvin
3208 Kelvin
4509 Kelvin
5858 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 495.06 nm to the first black body which has a peak wavelength of 669 nm.
1.4 : 1
3.3 : 1
1.1 : 1
1.8 : 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 81 times greater
it would be 9 times greater
it would be 1.32 times smaller
it would be 3 times greater
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Question 8
One end of a 58.7-cm copper rod (
a
= 385 W/mK) is placed in 100 grams of cold water at a temperature of 3.12 ºC. The other end is placed in the flame of a bunsen burner at a temperature of 1011 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
42.3 J/sec
4.9 J/sec
12.5 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 0.09 cm, how would the rate of conductivity be changed?
it would not change
it would increase by a factor of 11
it would decease by a factor of 0.300
it would increase by a factor of 3
it would decease by a factor of 0.0900
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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 76.90 cm, how would the rate of conductivity be changed?
it would be 3.2% as great
it would be 69% as great
it would be 9.6% as great
it would be 31% as great
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Question 11
A 350 watt immersion heater is used to heat a cup of water containing 214 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 3.22 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
24.8 grams
43.9 grams
15.6 grams
34.7 grams
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