Practice Problems
Heat Transfer Methods
Directions:
On this worksheet you will investigate properties of
the three heat transfer methods
.
omit
Question 1
Which method of heat transfer involves actual particles circulating from one region to another?
convection
conduction
radiation
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Question 2
Which heat transfer method can take place without a medium, that is, in a vacuum?
radiation
convection
conduction
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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 ºC. If the temperature difference drops to half that value in 23.9 seconds, what is the value of the decay constant, k?
0.0290 per second
0.0345 per second
0.0317 per second
0.0418 per second
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Question 4
At what time will the temperature difference equal 16.7ºC?
48.6 sec
60.6 sec
40.4 sec
35.8 sec
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Question 5
An incandescent black body has a peak wavelength of 492 nm when its temperature is 5894 Kelvin. What would be the temperature of a second blackbody radiator that has a peak wavelength of 309.96 nm?
6076 Kelvin
3713 Kelvin
10730 Kelvin
9356 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 309.96 nm to the first black body which has a peak wavelength of 492 nm.
6.3 : 1
2.5 : 1
1.6 : 1
1.1 : 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 9 times greater
it would be 3 times greater
it would be 1.32 times smaller
it would be 81 times greater
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Question 8
One end of a 54-cm copper rod (
a
= 385 W/mK) is placed in 100 grams of cold water at a temperature of 4.78 ºC. The other end is placed in the flame of a bunsen burner at a temperature of 1004 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?
39.2 J/sec
5.2 J/sec
13.4 J/sec
20.1 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 0.093 cm, how would the rate of conductivity be changed?
it would increase by a factor of 10
it would increase by a factor of 3
it would not change
it would decease by a factor of 0.0961
it would decease by a factor of 0.310
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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 75.60 cm, how would the rate of conductivity be changed?
it would be 16.0% as great
it would be 2.5% as great
it would be 60% as great
it would be 40% as great
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Question 11
A 350 watt immersion heater is used to heat a cup of water containing 196 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 3.23 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
23.9 grams
53.2 grams
67.3 grams
37.9 grams
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