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
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 54.2 ºC. If the temperature difference drops to half that value in 19.7 seconds, what is the value of the decay constant, k?
0.0352 per second
0.0284 per second
0.0508 per second
0.0298 per second
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Question 4
At what time will the temperature difference equal 8.1ºC?
53.9 sec
29.8 sec
80.9 sec
29.6 sec
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Question 5
An incandescent black body has a peak wavelength of 460 nm when its temperature is 6304 Kelvin. What would be the temperature of a second blackbody radiator that has a peak wavelength of 354.2 nm?
6670 Kelvin
4854 Kelvin
8187 Kelvin
6410 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 354.2 nm to the first black body which has a peak wavelength of 460 nm.
1.1 : 1
1.3 : 1
1.7 : 1
2.8 : 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 4 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 256 times greater
it would be 16 times greater
it would be 1.41 times smaller
it would be 4 times greater
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Question 8
One end of a 54.2-cm copper rod (
a
= 385 W/mK) is placed in 100 grams of cold water at a temperature of 3.94 ºC. The other end is placed in the flame of a bunsen burner at a temperature of 936 ºC. If the rod has a radius of 0.4 cm, then what is the initial rate at which heat is conducted along the rod?
56.3 J/sec
16.6 J/sec
33.3 J/sec
8.6 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 0.06 cm, how would the rate of conductivity be changed?
it would decease by a factor of 0.0225
it would decease by a factor of 0.150
it would increase by a factor of 44
it would not change
it would increase by a factor of 7
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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 71.00 cm, how would the rate of conductivity be changed?
it would be 9.6% as great
it would be 31% as great
it would be 3.2% as great
it would be 69% as great
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Question 11
A 350 watt immersion heater is used to heat a cup of water containing 192 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 3.06 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
43.9 grams
19.7 grams
55.4 grams
31.3 grams
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