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?
conduction
convection
radiation
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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 59 ºC. If the temperature difference drops to half that value in 20.9 seconds, what is the value of the decay constant, k?
0.0302 per second
0.0304 per second
0.0478 per second
0.0332 per second
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Question 4
At what time will the temperature difference equal 15.9ºC?
59.2 sec
41.7 sec
39.5 sec
31.4 sec
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Question 5
An incandescent black body has a peak wavelength of 668 nm when its temperature is 4341 Kelvin. What would be the temperature of a second blackbody radiator that has a peak wavelength of 440.88 nm?
6578 Kelvin
4568 Kelvin
9860 Kelvin
2865 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 440.88 nm to the first black body which has a peak wavelength of 668 nm.
1.1 : 1
5.3 : 1
1.5 : 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 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 3 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 59-cm copper rod (
a
= 385 W/mK) is placed in 100 grams of cold water at a temperature of 4.18 ºC. The other end is placed in the flame of a bunsen burner at a temperature of 955 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?
11.7 J/sec
4.6 J/sec
17.5 J/sec
45.0 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 0.081 cm, how would the rate of conductivity be changed?
it would not change
it would increase by a factor of 4
it would decease by a factor of 0.270
it would decease by a factor of 0.0729
it would increase by a factor of 14
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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 79.65 cm, how would the rate of conductivity be changed?
it would be 35% as great
it would be 2.9% as great
it would be 65% as great
it would be 12.3% as great
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Question 11
A 350 watt immersion heater is used to heat a cup of water containing 188 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 3.04 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
58.8 grams
33.2 grams
20.9 grams
46.6 grams
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