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?
radiation
convection
conduction
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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 54 ºC. If the temperature difference drops to half that value in 22.7 seconds, what is the value of the decay constant, k?
0.0441 per second
0.0312 per second
0.0305 per second
0.0327 per second
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Question 4
At what time will the temperature difference equal 16.7ºC?
46.1 sec
34.1 sec
38.4 sec
57.5 sec
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Question 5
An incandescent black body has a peak wavelength of 421 nm when its temperature is 6888 Kelvin. What would be the temperature of a second blackbody radiator that has a peak wavelength of 315.75 nm?
6994 Kelvin
7250 Kelvin
5166 Kelvin
9184 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 315.75 nm to the first black body which has a peak wavelength of 421 nm.
1.8 : 1
3.2 : 1
1.1 : 1
1.3 : 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 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 1.41 times smaller
it would be 256 times greater
it would be 16 times greater
it would be 4 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 4.54 ºC. The other end is placed in the flame of a bunsen burner at a temperature of 979 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?
9.1 J/sec
34.9 J/sec
17.5 J/sec
53.6 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 0.124 cm, how would the rate of conductivity be changed?
it would decease by a factor of 0.0961
it would increase by a factor of 10
it would decease by a factor of 0.310
it would increase by a factor of 3
it would not change
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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 73.98 cm, how would the rate of conductivity be changed?
it would be 37% as great
it would be 2.7% as great
it would be 13.7% as great
it would be 63% as great
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Question 11
A 350 watt immersion heater is used to heat a cup of water containing 201 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 3.26 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
50.6 grams
36.0 grams
63.9 grams
22.7 grams
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