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
radiation
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 54.3 ºC. If the temperature difference drops to half that value in 18.3 seconds, what is the value of the decay constant, k?
0.0379 per second
0.0264 per second
0.0546 per second
0.0291 per second
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Question 4
At what time will the temperature difference equal 15.7ºC?
27.5 sec
49.0 sec
36.4 sec
32.7 sec
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Question 5
An incandescent black body has a peak wavelength of 622 nm when its temperature is 4662 Kelvin. What would be the temperature of a second blackbody radiator that has a peak wavelength of 410.52 nm?
9860 Kelvin
3077 Kelvin
7064 Kelvin
4874 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 410.52 nm to the first black body which has a peak wavelength of 622 nm.
1.1 : 1
1.5 : 1
5.3 : 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 5 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 625 times greater
it would be 25 times greater
it would be 5 times greater
it would be 1.50 times smaller
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Question 8
One end of a 54.3-cm copper rod (
a
= 385 W/mK) is placed in 100 grams of cold water at a temperature of 3.66 ºC. The other end is placed in the flame of a bunsen burner at a temperature of 1016 ºC. If the rod has a radius of 0.5 cm, then what is the initial rate at which heat is conducted along the rod?
56.4 J/sec
14.6 J/sec
22.5 J/sec
64.9 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 0.145 cm, how would the rate of conductivity be changed?
it would increase by a factor of 3
it would not change
it would decease by a factor of 0.0841
it would decease by a factor of 0.290
it would increase by a factor of 12
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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 77.11 cm, how would the rate of conductivity be changed?
it would be 2.4% as great
it would be 58% as great
it would be 17.6% as great
it would be 42% as great
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Question 11
A 350 watt immersion heater is used to heat a cup of water containing 202 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 3.15 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
51.5 grams
18.3 grams
29.0 grams
40.8 grams
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