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
conduction
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 64.5 ºC. If the temperature difference drops to half that value in 18.6 seconds, what is the value of the decay constant, k?
0.0292 per second
0.0538 per second
0.0373 per second
0.0268 per second
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Question 4
At what time will the temperature difference equal 21.9ºC?
43.4 sec
28.9 sec
27.9 sec
41.4 sec
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Question 5
An incandescent black body has a peak wavelength of 644 nm when its temperature is 4503 Kelvin. What would be the temperature of a second blackbody radiator that has a peak wavelength of 373.52 nm?
7764 Kelvin
2612 Kelvin
12180 Kelvin
4774 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 373.52 nm to the first black body which has a peak wavelength of 644 nm.
3.0 : 1
8.8 : 1
1.1 : 1
1.7 : 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 6 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 1296 times greater
it would be 6 times greater
it would be 36 times greater
it would be 1.57 times smaller
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Question 8
One end of a 64.5-cm copper rod (
a
= 385 W/mK) is placed in 100 grams of cold water at a temperature of 3.72 ºC. The other end is placed in the flame of a bunsen burner at a temperature of 1028 ºC. If the rod has a radius of 0.6 cm, then what is the initial rate at which heat is conducted along the rod?
18.0 J/sec
23.0 J/sec
91.4 J/sec
69.1 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 0.204 cm, how would the rate of conductivity be changed?
it would decease by a factor of 0.1156
it would increase by a factor of 3
it would not change
it would increase by a factor of 9
it would decease by a factor of 0.340
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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 89.01 cm, how would the rate of conductivity be changed?
it would be 62% as great
it would be 14.4% as great
it would be 38% as great
it would be 2.6% as great
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Question 11
A 350 watt immersion heater is used to heat a cup of water containing 182 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 2.89 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
41.4 grams
18.6 grams
29.5 grams
52.4 grams
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